My Girlfriend Thinks She May Have A Cold Sore On

My girlfriend thinks she may have a cold sore on her mouth she says it was burning when she ate something with vinegar this evening for dinner we are in a lesbian relationship i have never had a cold sore ever. We were both tested for std's and HIV but I dont think herpes was 1 of the test she says she has never had a cold sore either..Ive noticed she does get pimples in close proximity to her mouth but they always looked like pimples no clusters are we panicking