My rashes are not healing, what do I do?

I get rashes a lot, usually heat rash. Or sometimes its from some sort of allergy. Anyway, they take for ever to heal. When I was about 9 I was allergic to the button on jeans and I had a rash all under my belly button for almost 2 years. Even when I stopped wearing jeans or taped of the button. I'm 19 now, and still my rashes take about 2 months to heal. They stop itching, but the bumps and scabs stick around. Is that normal? What could be a cause of this?