Intertrigo. Clotrimazole powder should do.
I doubt its eczema, it looks like nothing i searched.
It's excema dear, I. 16 and have had it since I was a baby. If you have cortisone cream put that in it and it will clear up overnight but if not you need to get a lotion called cetaphil (Walmart and Walgreens has it) and that is formulated to treat that rash. Just be sure to apply it every night and it will stay away.
Excema is just a rash caused by dry skin, lots of people have it so don't feel embarrassed. Hope I helped!!