What is this rash i have?

I have a rash on my groin area between my thigh and my scrotum. It itches a fair amount, and when i put hot water on it it itches more. It is more of a blister in the crevice and it becomes little pimply looking bumps that dont pop on the thigh. It has developed over the last couple days and i put hydrocortisone cream on it and it still kinda burns. i think it might be heat rash, but i'm also hoping it's not an STD because i havent had sex since november. Any idea what this could be?