Help! I need to know what’s going on

So TMI Alert but I need help...so recently I have discovered a rash on my inner butt cheeks near all my important body parts and it’s on both sides on the inner part of my butt. And I just got my period and usually things start to itch down there but I usually take a shower as soon as possible to solve that problem and I tried that recently but it doesn’t seem like it worked. And with the rash when I was taking a shower putting water on the rash made it burn. If anyone knows what this could be please comment down below!!!!!!!!!