Razor rash or something else? Please help!!

I've been really itchy down there for a while now. I've been tested for STIs and I'm clean. Is it from my really old underwear or the material? An allergic reaction ? Razor rash? I've tried using bepanthen and that only calms the itch it doesn't actually get rid of it. I've tried coconut oil and an Argan oil, again only calming the itch not getting rid of it. Help it's becoming so annoying and orating it's starting to hurt!