Severe knee pain ,any ideas whats wrong?

heya im 17 and i hit my knee off a Roller coaster 2 years ago. i damaged it really bad it was all bruised and hurt for over 2 weeks so i went to see my doctor. he supplied me with some strong anti inflammatory drugs which kinda helped but the pain returned and it got worse. so i was then told to just rest it and use ice packs to bring any swelling down and to keep it bandaged and to avoid putting too much pressure on it. so its bin 2 years ago now and it still hurts me.. i didn't go back to my doctor because all he frigging does is drug me up on anti inflammatory's which to be honest are no help to my knee. the pain still remains and i feel it is getting worse. I cannot walk up the staris without pausing because the pain is seriously unbearable its getting worse every time. and it also hurts when i run or sometimes when i am horse riding. i don't know whats is wrong with my knee im always in pain.. is it just something i will have to live with for the rest of my life or does anyone have any idea whats up with it ? please help xx