A rash on the buttocks/groin can be tinea cruris (jock itch), which can extend to the buttocks. But itching on the head of the penis (glans) is not necessarily the same condition. It can be balanitis from yeast, irritation from soap or condoms, eczema/psoriasis, or sometimes an STI. Recurrent penile inflammation may need STI testing and a blood-glucose test for diabetes.

Please arrange an in-person visit with a dermatologist, sexual-health clinic, or primary-care clinician soon, because this is chronic and involves the penis. They can examine it and, if needed, do a skin scraping for fungus, swab, STI testing, and diabetes screening. Tinea cruris often involves the inner thighs/buttocks but typically spares the scrotum, and topical antifungals are usual first treatment. Textbook of Family Medicine, 9e, p. 940.

Seek urgent care if you have penile swelling, pus/discharge, painful urination, ulcers/blisters, fever, inability to pull the foreskin back into its normal position, or rapidly spreading painful rash.

If you reply with whether the penile itching is on the glans, foreskin, shaft, or urethral opening, and whether there is redness, scaling, discharge, sores, or recent sexual exposure, I can help you understand the likely possibilities.

For ringworm on the buttocks and outer groin skin, a usual first choice is:

Before applying, wash gently and dry completely. Continue for the whole recommended course even if itching improves. The CDC notes that skin ringworm is commonly treated with antifungal creams for 2 to 4 weeks, depending on the product. CDC ringworm guidance

Because yours is chronic, see a dermatologist if it has not clearly improved after 2 weeks, keeps returning, covers a large area, or has spread. You may need a skin test and prescription tablets, but do not start oral terbinafine, itraconazole, or fluconazole yourself because the right medicine depends on the fungus and these drugs can interact with other medicines and affect the liver.