It could be a fungus maybe -- no one has prescribed antifungal creme? Actually, come to think of it, I think Vagisil is an antifungal creme. You need a good dermatologist, not a lot of guesses from the moms on this site.
I'm surprised this has gone on this long. You need to get on the phone, right now, and see doctor after doctor until someone takes care of this. There is absolutely no reason you should keep suffering like this, and these doctors are way out of line to keep letting you endure this.
DO NOT be embarrassed, no one will think you were the cause of this. Skin things happen.
In terms of the scar, it's probably a pretty surface scar if it's from scratching, and maybe even something like Retin A could help remove it, but you can't use anything like that until you have gotten rid of the underlying problem. Clear up the rash first, then take care of the scar.
Hopefully you have good health insurance, so while these inept doctors are taking your money you can keep going until you find someone competent who gives a damn.