E-P when i was in primary school my right shoulder got dislocated, but i have never had any problem with it since. That is very interesting though. do you think it could be more joint related then?
For me, yes, I think that was the case. It is so long time ago I was told about it that I can't remember. I was years ago in physiotherapy about my knee and then she also had a look on my shoulder as I mentioned that it is slightly dislocating when I move my arm at shoulder height back and forth. She examined it and told me very seriously that I have to do some work-out to get more muscles to "pull the shoulder more together" or after my 40s I won't be able to write any more (and that it'll need a surgery), maybe slight exaggerating but still I took it quite seriously. I did little exercise but then forgot the whole thing (=the average stupidity of human nature). Anyway, when it started to disturb my new running hobby I really had to start to do something about it
Well, I am glad I did because now my shoulder won't hurt any more during the runs, I it feels generally better than ever and my upper body doesn't get so tired in long runs.
Hopefully it will work for you too. At least you have nothing to lose if you add some upper-body exercise (and maybe some core as well, although nothing to do with your shoulder) to your weekly routine.