Hello, I Have Had A Recurring Rash Along My Waistline

Hello, I have had a recurring rash along my waistline and where my inner thigh meets my groin. The rash consists of red spots, no itching or discomfort, not raised, no crustiness or scaly feel. It seems to spread a few inches and last anywhere from 2 weeks to 2 months at a time. My doctor treated it as tinea versicolor, and while it did disappear, I believe it disappeared only because the rash was at the end of its course, because it has come right back. This has been a recurring rash for a few years now and I am becoming desperate for a solution.