Has anyone had vagina chafing?

When wearing gym leggings, I don’t wear underwear. Recently, I’ve been doing lots of vigorous exercise in said leggings, and I noticed recently a lot of concentrated pain in my labia, similar to chafing. Upon inspection, I have a sore red firm spot on my labia which is super tender to touch, and hurts when I walk regardless of what I wear.

I’m 99.99% certain it isn’t an STI as I’ve been with my healthy partner for 4 years, plus we haven’t had intercourse in about a month.

The pain of this sore is really getting to me, and I don’t think I can possibly have sex with it still around.

Has anyone experienced “chafing” on their labia before who can recommend a treatment? Or should I be going to a doctor ASAP?

Thanks ladies!