I think something's wrong with my body HELP!!!

Okay so I was recently on the depo shot for about 3 years, my last shot was January 7, 2014 and I haven't had one since.. My period started about mid September it only lasted for about 3-5 days then it was over with that happened about every other week and my boyfriend and I have been having sex without a condom even right after my period and I'm not pregnant not saying I'm trying to conceive but what's wrong with me that I'm not pregnant I know nothing is wrong with him cause he already has 2 kids and I have none the doctor  said I'm just lucky but I wonder if something is wrong with my body on why I'm not pregnant yet??