I am dealing with the same thing. It came on suddenly about 5 years ago. I’ve torn a tendon in my shoulder, Achilles, elbow, and hip. Tendinitis throughout my body. I was working with a trainer and very fit, doing things properly. There was speculation that I was over training. I’ve done all these things and nothing has helped. In fact now I have plantar fasciitis and both my Achilles burn from time to time. My muscles knot up when I exercise and I have a massage therapist who is also baffled. My shoulders both burn if I do any type of weight training. I’ve been tested for everything under the sun. Interesting that I’ve found another woman that has the same symptoms.