I've rashes especially on butt n my legs since a year ago. I've applied different medicine since then but none works. What could this be?

Groin Rash. The area between the buttocks and the upper inner thighs, is warm and prone to friction rubbing. It is a common place for a fungal infection, called dermatophytes, and also yeast infections.Other kinds of rashes can also affect these areas, like psoriasis, and dermatitis. A year is a long time, and so it may be best to see a skin doctor, who can make the diagnosis and prescribe the right medicines.
You need an exam. You should see your primary physician or a dermatologist. If a lesion is not responding to treatment, a simple skin biopsy can help make the correct diagnosis.