Hello and thanks in advance.

About six years ago I injured my shoulder, I was running and pushed on a door I thought was unlocked but was not.
The problem: I could lift my arm straight up but not at any type of angel and no fast movements. I could lift my arm to a point but then had to rotate my shoulder a little before I could lift it all the way. They originally thought that the muscle was rubbing against a bone (and that is what it feels like) I had x-rays and a MRI both showed nothing. After six months of pain and test I was given a cortisone shot which helped right away. About a year later the problem returned but not to the same degree. After playing sports or working out the shoulder would become sore and the next day I would not be able to lift it and no fast movements. I have lived with it as it was manageable but recently it has become very painful again. I wake up every morning with a sore shoulder some days worse than others. No fast movements and no heavy lifting and pain when moved in a certain direction and angel. I had another Cortisone shot but it did nothing.
I had another MRI and they injected dye in first. Again the doctor tells me that there is nothing and I just have to live with it.

I can't do sports, I am starting to lose strength in the arm.

Part of the problem is it is hard to figure out exactly where the pain is coming from and when pressing or digging into the shoulder there are no sore or painful spots.

Two questions: Do MRI's work on everyone as they don't seem to work for me?
I had knee problems two years ago, had an MRI it showed no real damage. But when I had exploratory surgery the doctor tells me I had two tears in my meniscus.

Any idea what could be wrong with my shoulder?

Thank You

Rod