Why does intercourse hurt soooooo much???!! :-(?

Ok, im 15, have been having sex for the last year and a half now. I have a boyfriend who is 18 and we have been dating for more than 9 months now.. I have a problem though, and its ruining my sexual relationship.. or atleast for me it is. We have sex about every weekend and sometimes in the week too, if we can. And usually in one day, we have sex about maximum 3 times. My boyfriend isnt unually endowed very big so thats not the answer, hes dick is normal size, perfect size. In the begining it was fine though, i had no problems and everything was great. But about 3 months into our relationship, i started experiencing a stinging,burning,tearing feeling when he put it in me, and the pain lasts for about 5 seconds then all will be fine and it would feel great but if i could discribe it, it always feels like the pain is coming from only the left side of the opening for my vag :/.. Plus usually if we have sex more than once a day, the second time that we do it in that day, my vag feels reaally raw and it burns at my vaginal opening, and i wouldnt also naturally be able to get wet, so we have to use lube.. but it still hurts then!!! Also sometimes, after we had sex, i would go to the bathroom and then id see that i bled abit, just a little but sometimes it looks like a piece of skin from inside that came out!!Its usually pinkish and very small and thin, but wtf does that mean!!??I am on depo provera injection for the last year now, only have my periods about for two days every 3 months, which i have no problem with, i prefer it that way. Also, i have recently been experiencing alota discharge, which i didnt always have. It dusnt look or smell funny, just the amount has gotten more. So these signs.. is it cervical cancer? could it be a vaginal infection? Bladder problem? Is it maby cause im so younge and my body isnt ready for sex? maby because we do it too much? Is it just damaged tissue inside that cant heal that easily? Anyone that has answers, real ones that make sense, please try and help me!? Id really like to enjoy sex as much as he does, and i cant find the answers to get it right. Btw, dont tell me to go to the gyno cause thats not a option, i cant because of my parents and i also dont know wherre and dont get my own money and getting there without my parents knowing would be really tricky... I need a at home solution.. Please help, anyone?? :-(