Sore

Me an my fella have been goin out now about a year we recently have been having sex the first few times were fine but the last 2 times it has got really sore I have te get him to stop an im nearly in tears with the pains be buckled over on the bed!! The pains are in my lower stomach an get sharp pains in my bum aswel they last fer the rest of the day an a bit of the next day i be sore!! But i cant work out why!! Im 17 an i dont know wat is wrong i have only had 2 partners We chatted about it an the last 2 times it has hurt has been with in the space of a week my period is due I was wondering could it be that my period is due?!!Or maybe that i needed to go to the toliet?? We haave got a bit more adventous aswell an i was wonderin could it be that Any help would be greatly appreicated!!?