well i know for sure its not a std.trust me my hubby is a freak and is the most faithful.i know people are like you can never be too sure..but really this hubby of mine-its so hard to explain-but hes too afraid to cheat and therefore get an std.also hes afraid some other guy is gonna sweep me off my feet.we both dont even have time to do it even if the opportunity arises.
something similar happened to me. when me and my boyfriend had sex for the first time it burned. it scared me because i thought it may be an std i had got from him. i know i didnt have anything ten days before having sex with him because i got tested. someone told me it may be due to dryness but that has never been an issue with me before. so i told my doctor about it and she told me to come back in a month for std testing. so if you havent had an std test you may want to try that.
I was prescribed a estrogen hormone cream made especially for vaginal use. It really helped to relieve the irritation and dryness. Perhaps mention this to your gyno. and see if this might help you.