Why does sex with him hurt

ok so here is the thing ... whenever me and my boyfriend have sex i always have to start on top to ease in because it hurts soo much to the point sometime where it actually brings tears to my eyes. and then a couple of thrusts later im fine i dont have any pain during but after we are done and ive come down from my high it really hurts. Most of the time i have to pee afterwards and then when i go to wipe im bleeding a lil and im guessing thats from being torn a lil i dunno. Anyhoo the vaginal pain is not on the deep inside but right near the opening. This pain by the way can last from 3 hrs to 2-4 days!!!
What the heck is wrong with me please tell me

---oh and i know i dont have STDs ive been with him for 7 months and on the sixth month marker i went and just to make sure i tested for it nope im clean
no warts, and its not a yeast infection either
and its been like this the pain that is since we first started having sex last sept 2007.

like i said i would really like to know what is wrong am i too small for him or what???