Sorry if this is tmi ladies but there are times where my boyfriend & I have sex & my vagina starts…

Sorry if this is tmi ladies but there are times where my boyfriend & I have sex & my vagina starts to have this burning sensation during and afterward. I know I dont have an std & my bf knows he doesn't either... Its weird because this only happens during certain positions or when he rubs up against me the wrong way. I mean for all of my appointments they take a urine sample so if anything was wrong they would know & tell me. Has any of this happened to you? I see my doctor Wednesday so I plan on asking him what's wrong.