the first time i had sex (and a lot of times when it's the first time after it's been a while) i got a wicked yeast and/or bacterial infection, and it seems like one of those may be the more likely explanation. the vag just always doesn't love it when things like penises come crashing in and disrupting its delicate chemistry, you know? either one is more an annoyance than something to worry about, anyway, but you might want to go get swabbed and find out what you're dealing with, if only so that you'll recognize it in the future.