What your reports show

• Red blood cells: 10 cells/µL, where the reference is negative. This is microscopic blood in the urine.
• Calcium oxalate crystals were noted.
• No protein, glucose, nitrites or white cells, so there is no sign of a urine infection.

• No stones were seen and there is no hydronephrosis (swelling of the kidney from blocked urine).
• The renal sinus is "compacted with small hyperechoic inclusions" on both sides. This means tiny bright spots in the centre of the kidney. They can be tiny crystals or sand, but ultrasound can't say what they are.

• Early fatty liver changes and non-specific pancreas changes. These don't explain this kind of pain.
• Blood count and ESR are normal. Your white cell count is 9.57, a hair above the upper limit of 9.5, which means little on its own.

Why you can still have pain

• Textbooks describe renal colic pain as referred from the loin and radiating to the groin, with hematuria and a clearly colicky character - S Das, A Manual on Clinical Surgery, 13th Ed; Sleisenger and Fordtran's Gastrointestinal and Liver Disease.
• A normal ultrasound doesn't exclude a stone. It often misses small ureteral stones, and it can't see the ureter well. Hydronephrosis only shows up if the stone is blocking urine flow. A low-dose non-contrast CT KUB is the better test if symptoms continue.

• Muscle or spine problems, such as lumbar strain, a facet joint, or an irritated nerve (ilioinguinal or iliohypogastric). These cause pain that goes from the back around to the lower abdomen.
• Constipation or irritable bowel.
• Inflammation of the lymph nodes or the end of the small bowel.
• A small inguinal hernia.
• Testicular or epididymal problems, which can be felt in the lower abdomen. A testicle exam matters at your age.

What I would do next

• Repeat the urine test with microscopy in a few days, and drink plenty of water meanwhile.
• If pain keeps coming in waves or the blood in the urine persists, ask your doctor about a low-dose CT KUB. If you pass a stone, strain your urine and keep it for analysis.
• Ask for a proper physical exam, including the abdomen, back, groin and testicles, because these often find the cause when tests don't.

Go to the emergency room if

• The pain is severe or getting worse, or it localises to the lower right abdomen.
• You have fever, chills, repeated vomiting, or visible blood in the urine.
• You can't pass urine.
• You have testicular pain or swelling.

Why this pattern points to a stone

• Ureteric colic comes in waves. The ureter tightens and spasms around a small stone, and the pain peaks and then settles when the stone shifts or moves on. Episodes can last from 20 minutes to a few hours, with pain-free gaps in between.
• It fits your location. Pain that runs from the right back or loin down to the lower abdomen and groin is the typical route of a right ureteric stone.
• It fits your tests. You have blood in the urine, oxalate crystals, and small bright spots in the kidney. A small stone or sand can cause real pain without blocking urine flow, so the ultrasound can show no hydronephrosis.
• The pain may have stopped because the stone moved. It may have passed into the bladder, or it may be sitting in a position that doesn't block urine for now. More attacks are possible over the next days.

Why appendicitis is less likely

Other causes of severe pain that settles

• Intermittent testicular torsion can cause sudden severe pain in the lower abdomen or groin that resolves. At your age (about 20) this should be checked. Look for testicular pain, swelling, or one testicle sitting higher than the other.
• Biliary colic is possible, but your gallbladder looked normal on ultrasound and the pain site is wrong for it.
• Bowel spasm or constipation is possible but usually causes milder pain.

What to do now

• Drink plenty of water, about 2 to 3 litres a day unless a doctor has told you to limit fluids.
• Strain your urine and keep any stone or gravel you pass, so it can be analysed.
• Ask a doctor about a low-dose non-contrast CT of the kidneys, ureters and bladder (CT KUB) if the pain returns. It is much better than ultrasound at finding small ureteral stones.
• Heat on the back or flank may help. Ask a doctor about painkillers such as an anti-inflammatory (NSAID). Avoid them if you have stomach ulcers or kidney disease.
• Repeat the urine test with microscopy in a few days. If the blood in the urine is gone and the pain has stopped, a stone has likely passed.

Go to the emergency room now if

• The pain does not settle, or it comes back severe and you can't control it.
• You have fever, chills, or shaking, because a blocked and infected kidney is dangerous.
• You vomit repeatedly or can't keep fluids down.
• You can't pass urine, or you see heavy visible blood in the urine.
• The pain moves and stays in the lower right abdomen, or you can't stand being touched or moved there.
• You have testicular pain or swelling.

At home while you're pain-free or have mild pain

1. Drink plenty of fluids. Aim for about 2 to 3 litres of water a day, enough to keep your urine pale. Don't force huge amounts during an attack, because that can make the pain worse.
2. Strain your urine through a cloth or fine sieve and keep any gravel or stone. Take it to the doctor for analysis.
3. Stay active. Walking is fine, and bed rest isn't needed.
4. Use heat. A warm pack or warm bath on the right back or flank can ease spasm.
5. Eat normally. If oxalate stones are confirmed, avoid large amounts of spinach, nuts, chocolate, and strong tea. Don't cut out calcium, since normal dairy intake actually helps. Keep salt low.

If the pain returns

• Anti-inflammatory painkillers (NSAIDs) such as diclofenac or ibuprofen work best for stone pain. Take them with food, and ask a pharmacist or doctor for the dose. Avoid them if you have stomach ulcers or kidney disease.
• Paracetamol is a gentler option if you can't take NSAIDs.
• A doctor may add an anti-nausea medicine, or in some cases an alpha blocker such as tamsulosin to help a stone pass. The evidence for tamsulosin is mixed, so that is a doctor's decision. Don't start it on your own.

See a doctor in the next 1 to 2 days

• Take these reports and ask for a urology or general physician review.
• Ask about a low-dose non-contrast CT KUB, which finds small stones that ultrasound misses.
• Ask for a repeat urine test with microscopy. A blood test for kidney function, calcium, and uric acid may also be useful.
• Most stones under 5 mm pass by themselves within days to weeks. Larger stones may need a procedure.

Go to the emergency room immediately if

• The pain is severe and doesn't settle with painkillers.
• You have fever, chills, or shaking.
• You vomit repeatedly or can't keep fluids down.
• You can't pass urine, or you see heavy blood in it.
• The pain stays in the lower right abdomen and gets worse, which could mean appendicitis.
• You have testicular pain or swelling.