And now hes accusing me of cheating and I didn't and never would even think about it

Well my first thought is a yeast infection. Or if you hadn't showered since you guys last had sex it could just be left over sperm or your natural lubricant. I sometimes get that from my toilet paper! Tell him to learn more about the female anatomy before accusing the ridiculous stuff. 

It's probably just a yeast infection/thrush. Not an STD. Go to the pharmacy for some cream but if it persists go to the doctor. Don't stress about it. Even babies get thrush and your mum has probably had it a few times in her life so you should be able to talk to her about it if you are too young to get treatment yourself. The bigger issue is why is your bf so quick to accuse you of cheating. That is a huge red flag. Be careful of jealous boys/men. They often have trust issues and become very controlling. does he trust you about other things? Please be careful. Trust is crucial to relationships. You don't need to put up with false accusations. It will drive you crazy. Take care