I figured out that going for MRIs and other diagnostic tests pretty pointless as they find it difficult to say for certain what happened. In my case if it had been discolated this wouldn't change the outcome as there is no treatment apart from wait and then buold up exercise again.

When i was researching i learned that any action that raises the hand above the height of the shoulder rotates the SC joint so I avoided those movements as much as possible to give the SC joint rest. Is your SC joint lower/higher/ more/ less prominent than the other? Maybe it's your AC effecting your SC. I think mine was SC dislocation as I had little/no issues with my AC joint/ shoulder.

If were going private/ NHS I'd try and see a SC/ AC joint specialist.