ulcers, & I'm scared

So I have been sexually active for 7 yrs and have never had any problems down below... Until recently. I had sex one-day and realized it kind of burned when we finished, I thought maybe we got to rough. I.checked my self the next day cuz I was hurting. I noticed the inside of my vagina was slightly red and irritated but it went away. Then we had intercourse again and the pain.came.back. same spot. It turned into what looks like to me as a.canker sore. 2 days is been this way and I noticed 2 more sores inside my vagina. It really hurts to Pee and walk, sit run.  I'm so scared as to what this means or is. Anyone.can shed some light to me would be greatly appreciated. P.s. the guys I've been with have come back with clean medical check ups.

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