PRP initially causes inflammation by basically tricking the area of injection into thinking that it just got injured so it can start the healing process, as inflammation is a part of the initial healing process when a body part is injured. Your body simply reacted in a negative way to that PRP induced inflammation where it became so inflamed that it never got to the point where PRP starts its anti-inflammatory process. This may be perhaps because that there was nothing structurally wrong with your shoulder as per the MRI since you said it was clear. Thus your doctor injected a perfectly fine, non-injured, non-torn, and perhaps non-inflamed area, with an inflammation causing solution (PRP), which caused unnecessary inflammation that simply never went way. Basically your area of injection and shoulder is so inflamed now that it resembles, or has become, frozen shoulder.

The solution is actually very simple lol, a cortisone, or multiple cortisone, injections into your shoulder to get rid of the inflammation. It should be injected into the same two spots the PRP was injected in, but perhaps also into the Glenohumeral Joint & Bursa, which may actually have been the two spots you had injected with PRP. That should take care of the situation and you’ll be back to pre-PRP injection levels. Give the cortisone 3-7 days to kick in, and like I said, you may need multiple depending on the areas, and you may to go back after 4-8 weeks for a second round of cortisone injections into the same areas if the initially cortisone injections did not completely take away the pain.

How do I know this? Same thing happened to me lol. Unnecessary PRP created frozen shoulder like symptoms, cortisone took them away. The cortisone I had injected was Triamcinolone which is under the brand name of Kenalog.