I think i have dermatitis but don't know how to treat or be positive ?

Dermatitis is a: general term to describe inflammation or infection of the skin. It does not really give me an idea of what type. Most of the cases of skin inflammation are caused either by hypersensitivity (allergy) or infection. If it is severe you can try an antifungal ointment or cream (like Lamisil) first then if not successful try a steroid (like hydrocortisone) over the counter.