from my experiences... the most important thing, before you really start exercising shoulders, is to find out/learn if your shoulders are sitting right, where/how your shoulders are supposed to sit-
what I thought was 'normal shoulder position' turned out to be "shoulders more out than in their sockets"
and that a.o. had caused previous shoulder exercises to be inefficient and painful
if you look in the mirror and there is a big 'gap/hole' between the collarbone and 'top of shoulder' ... it apparently is likely that your shoulders are 'out of their proper place in socket'-
I had to first learn a "pull shoulder slightly up- push backwards- drop shoulder- see the big gap disappear" maneuver and then learn with which muscles to hold the shoulder in its right place (small ones on and to the side of back- not pecs and trapezoid which was what I was doing)
just a 'cautious' thought
oh shirley- if you are still around- have you got acid reflux? - meds for acid reflux (like omeprazole/lansoprazole) are also often prescribed to go with longer term nsaids use as they seem to help protect against its ulcer causing effect.