pain with sex

okay so when my boyfriend and I have sex the first time I feel no pain; but if we try to the next day I have pain when he puts it in, not like in my vagina, but on the outside, like little cuts, it burns. could this just be from friction from the last time and bad lubrication. i have no strange discharge and I know it's not a yeast infection, so what else could it be? neither of us have been with someone else and we've always used protection. if anyone else has had this problem, how did you fix it?