Hi, thanks for writing HCM.
From the given description, I feel that the cause of your pain in shoulder and collar area is due to sudden, unaccustomed strain of the involved muscles.
I suggest you to increase the frequency of gym exercises in a GRADUAL MANNER so that your muscles get acclimatized. I am sure that you will regain your normal strength as before over a period of time.
The temporary management of your muscular pains is as follows -
* Rest to the affected part and don't involve in activities which puts additional burden on the strained muscles.
* Ice packing to alleviate acute pain.
* Once the acute pain subsides, moist heat fomentation to relax the muscles
& muscle relaxant
medications as needed
Hope this information is helpful. Good day