Tendinitis is caused by overuse, or a rapidly increased use, of the affected muscle/tendon/ligament group. Connective tissue needs to be strengthened and toughened over time with a slow increase in the level and duration of the stresses that are applied to the group. As stress is applied, there are micro-tears, cellular damage and other processes that tend to temporarily weaken and inflame the tissues. The rest periods between the application of stresses allow our bodies to repair these minor injuries while telling our bodies that those areas need to be strengthened. If done properly, we will be able to sustain greater stresses over time without long-term injuries. When we over-stress the tissues to the extent that normal repairs cannot be easily made by our bodies, or when we do not allow sufficient rest periods for repairs to take place before we re-apply the stresses (over-use),the inflammation cycle takes over such that inflammation causes additional damage, then the additional damage causes more inflammation, and so forth. The only things that work to get rid of the problems are to decrease the inflammation and allow a stress free period for the tendons to heal. As others have suggested, steroids (like hydro-cortisone), other anti-inflammatory drugs, physical therapy, and other medical intervention is often a big help. Once you break the cycle by reducing inflammation, healing can begin. No matter what, you will have to limit your activity with the affected muscle/tendon/ligament group until healing occurs. After that, start with low weight, low repetition, low frequency exercise and build up VERY SLOWLY. It can take up to 2 years to get everything functioning at full strength, and that assumes you do not keep re-injuring yourself. This applies to all forms of tendinitis, including things like "shin-splints" and "tennis elbow".
I recommend starting back your exercise program after you have healed using something like the "Bow-Fit" exerciser rather than actually using your bow, because you can start at a very low weight and increase it as you progress, something you can't do with a real bow. There are several models of the Bow-Fit in various weight ranges. I would recommend that you start with the medium model (or even the light model if your draw weight before was low) and later work back up to the heavy model (or the medium model). I have the heavy and the safari models, but I have not yet built up to the safari model. Each Bow-Fit is only $20, so it is not a big expense. They are also good for the warm-up and stretching that we need to do before we shoot our bows. There is a kit that also includes a DVD along with the Bow-Fit. I bought the kit and found the DVD fairly helpful but not exceptional. I think they could have done a better job showing how the Bow-Fit can be used to its full potential.
I have no financial interest in Bow-Fit. I have come back from serious health problems and found this simple device to be very helpful in getting me back into shooting. A few months ago I could barely draw a 45 pound bow to my anchor point. Now I can draw (with some difficulty) a 70 pound bow to full draw. I did this with no significant injuries, just a little muscle pull in my lower back muscles that lasted less than two weeks.
Resign yourself to your injury, seek medical care, allow a significant period of inactivity for healing, and then start easy and progress VERY SLOWLY using low draw weights, plenty of warm up and stretching, and very minor increases in weight over a LONG time. Make sure to strengthen your other muscles too, because they provide the stability that is necessary to prevent injuries and allow your body to function correctly in your shooting activities. If you do something different you will probably re-injure yourself and be forced to start all over again. Patience is difficult but necessary. Good luck.
Allan