How to diagnose or cure my joint pain?

[venus123zx]

Sorry for my english. It is not my mother tonge.
Around one year ago I started to experience a slight pain in my shoulders. It would be mildly painful to make some moves, especially when I had to lift some weight. For example, doing shoulder elevations holding some weight, of internally rotating my shoulder.
One day, after my triceps workout, the pain increased severely. It would be painful to lift my arms even without any weights. Also, my shoulders would crack and pop when doing internal rotation and elevations.
The doctor ( shoulder  and elbow surgeon) ordered an ultrasound, that showed a slight subacromial bursitis in both shoulders. He said that that was not really significant,  since that small swelling of my bursas could not explain my sypmtoms.
However, he sent my to physical theraphy, that after 20 sessions showed no result. Then, I got a corticoid injection on both shoulders, which reduced  pain considerably but not completely.
Then, the doctor ordered a MRI, which again showed an incipient bursitis on both shoulders. I did more physical theraphy and I got another cortisone injection on each shoulder, but I did not notice any advancements since the first two injections.
Some months later, my elbows started to hurt. It would be very painful to push something or even to pull the car belt downwards. Also, it would hurt to touch the very tip of my elbows. I went to the doctor again, and  he ordered an ultrasound and a MRI for my elbows. Also, he ordered a MRI using a contrast agent for my shoulders.

To my surprise, neither the ultrasound nor the MRI showed no injuries in my elbows, and, the MRI with contrast agent, showed no injuries in my shoulders. Not even the sligh bursitis was present-

He also ordered some blood tests, like PCR, rheumatoid factor, CRP, and other tests whose name I do not remember in the moment, that were suposed to detect any Autoimmune disease. However, all of them had a negative result.

So now, I still feel the same pain in my shoulders when I try to lift some weight. And the cracking and popping are still there. The pain in my elbolws has reduced a little but I still experience it if I try ti push something heavy or if I touch the tip of my elbow. According to the doctor, it looks like a tricep tendinitis. (but that is not the case).

are there any other tests?
what could it be?

Thanks a lot