Does anyone recognise this rash?

DISCLAIMER: I WILL BE VISITING MY DOCTOR I JUST WANT TO KNOW IF ANYONE HAS HAD THIS.

I'm 19 and I first noticed this rash when I was around 14 years old? I first noticed it on my shoulder in the shower and I thought there was some orange water that had splashed onto me which confused me haha. I don't have it on my shoulders anymore but I do have it in a small area under my bra strap, under my boobs, in my bikini line and above my vulva/vagina on the pubic bone.

It changes quite a bit but I've not noticed any pattern. E.g. It used to be a lot worse under my boobs but now it's just the one patch.

It's always visible, turns a little more red after a shower and isn't really raised. I remember rubbing/scratching it at the start thinking it was something just on my skin and it went bright red and stung like a bitch, it felt like a carpet burn sting and it was horrible :/

I've tried changing my body wash multiple times, I use soap-free and I wash often. I tried this magnesium-cream-thing someone told me to try a couple years ago and it cleared the patch I used it on but because it changes anyway I don't know if it actually helped but it was painful to use and annoying having to air out the area for a while afterwards.

I've been considering becoming sexually active so I want it checked out and cleared by a doctor obviously but I was just wondering if anyone here has had anything similar? It doesn't really affect me which is why I've left it so long to see a doctor but obviously it's important to get rid of it if I'll be having sex. I was just wondering if anyone knew what it was because I've always found doctors pretty useless when it comes to skin problems I've had in the past so it would be useful to know what it might be.