Does it travel to the bicep or shoulder at all? Can you trace the arm pit pain back up to the collar bone.
A new activity sometimes flares. I had a fall onto the heel of my hand and sent zinger pain. It was bad in the forearm, not the worse is the armpit and splits up to the collar bone, around to the bicep.

Reaching to brush my hair, driving flare the arm pit collar bone to neck bad,

I have been toying with another trigger in the area along my shoulder to the neck that is painful. In the meantime, the doc gave me metropropal maybe it was, a steroid, calm some not go away.

So I manage it with regular coated Aspirin. Moist heat, rest.
Hope it calms down soon,
di