Pain During Sex. PLEASE HELP!

claudia
Hello everyone, I REALLY could use some help here. My boyfriend and I have been together for a year and a half, and we are both 16. I'm young, I'm healthy, and we are very safe when having sex and also use water based lubricants. 
However, almost every single time we have sex, I get a terrible stabbing pain in my lower abdomen when he thrusts deeply, it feels like he's hitting something, and it's very painful, sometimes I'll cry. Of course, this makes him feel bad and it's ruining our sexual aspect of our relationship.
At first I thought it may just be because I wasn't "turned on" enough to have sex, and maybe it had something to do with my cervix? I've done research, and some say this could be caused by "endometriosis", "uterine fibroids" or "ovarian cysts". 
Of course, reading those suggestions as to what is causing my pain makes me very worried and scared. Again, I'm only 16, and I don't know what to do.. If you have experienced this before, and have suggestions as to how to make sex feel better, or even suggestions as to what could be causing this, PLEASE PLEASE PLEASE comment! I'd really appreciate anything. Thank you.