Are you using condoms? Have you changed brands at all? I know the first time I used them I was fine, but the second time I had a reaction. Switched to the sensitive kind and had much better luck.
If this doesn't seem like the problem, and the things sweatpea said aren't the cause, then I agree and say that you should contact your gyno and just have a check-up. It never hurts to make sure things are in order, esp. being somewhat 'new' to being sexually active. It could just be small tear in your vaginal wall, which I have had happen from my bf nails while he was playing around down there...sounds unpleasant I know, but these things can happen, and if that's the case it just needs time to heal, but you will want to make sure it's not infected.
I hope that helps.
