After you have notice these lumps did you go back to your Doctor? This should be the first thing you should do. It sounds like you might have developed an lactic acid build up, Having dealt with a shoulder injury and having to where a sling too. I tried many thing to help improve my healing process. The thing I found that work the best was trigger point massage, but to go a therapist was costing me way too much and the visits where too far apart. So I ask the therapist if her could show me some self-trigger point massages that I could do myself to maintain his treatment and to help with the healing process. So I would heat the area first then self-massage just to loosen the muscles and bring blood to the area then I would go into the self-trigger point massage and yes sometimes it hurt like hell when I did it but I knew that it was just letting me know that it was releasing the knot and the next day or the day after I would feel a lot better and the pain would be gone along with the knot. Then after I did the self-trigger point massage I did self-massage again to help the body remove the waste that was in the knots. Then I would ice the area. I would that my experience will help you. Take care, there is always someone out there that care!
The best to a healthier,happier, and pain free you!