Painful!!!!

OK ladies help me out! Me and my husband have been ttc for almost a month and we have been bd since we first got together! OK so last night we go to bd and I was on top and when he put it all the way in it hurt like I jumped up and he asked what was wrong? Since we been together I haven't felt that pain. Sorry for the visual but it was like we was "doggy" style and he was power driving it but we wasn't. Like I said I was on top. Why do u think that could have happened? Whats up with that!?!?!