Swimmers Shoulder

I’ve got pain around supraspinatus/lev Scap area of my left shoulder that also radiates down my arm laterally.

It is irritated by a hard swim (freestyle) or any activity involving abducting my arm when using resistance ie: lateral raises and shoulder press both produce pain which seems to come on afterwards.

I’ve been stretching by pectorals to relieve the stress on my shoulders, and have started doing backstroke and breathing bi-laterally.

There seems to be a number of possible explanations ie tenonitus or impingement. Can anyone throw light on this or have they a similar problem, and how did they rehabilitate? A week off seems to alleviate but it soon returns. Thanks Mark