Hi uni, this was a huge problem for me for nearly twenty years. I used to do computerized bookkeeping. I developed severe wrist pain, then arm and hand pain, and finally finger pain - which then spread to other points over my body, anywhere that had static muscle load. Repetitive action, as well as static muscle load, seem to be able to trigger what I think of as local PEM - its not the whole body, just the muscles involved in the activity. If the aggravating action is continued long enough it can cause damage. In my case I tried physiotherapy to correct it (in the 80s) - big mistake. I think that locked it in as semi-permanent damage.
I do not regard your symptoms as unusual except in once sense - I would have expected it to be more common, and it doesnt appear to be.
Bye, Alex