Sores??

I have been tested for STIs/STDs and it's negative. I've only been with one guy who's also been tested. But since June, I've had these little open sores around my opening. They sting/burn when touched, and when I'm having sex. Sometimes they heal but they come back. They often bleed when I wipe too. Any reason that isn't an STI? I'm seeing a gyno late next month but sometimes just getting other opinions beforehand is nice too...
P.S. My boyfriend never gets them either and I occasionally got them when I was a virgin.