My terrible knee pain is not going away for 5 years now. Doctors cannot help.?

I went to many doctors and all they say is that you do rest and be in motion, the problem will take care of itself. They did X-Rays but they appear fine. They recommend MRI which is too expensive. One doctor said depending upon the prolbem they might do surgery but another doctor is against surgery. The gel in my knees seems to be collapsed to me, thats why I am feeling massive grinding sensation. I cannot sit down on my feet, it would pain hell. I cannot walk for long. I cannot run for long. I cannot bike uphill or walk uphill. I cannot ascend stairs normally. Can you tell what is the name of the disease that I am having? All I know is the grinding sensation in my knees and nothing else.