stop masturbating!

Sorry. I use other hand

you don't use both?
lol, sucks to be you little man

lol, what Smegma said, though honestly just take breaks and stretch, I find it works for me.

In this case it depends on where the pain is actually coming from, which is difficult to diagnose over the Internet. The pain could be from a number of sources. I would suggest massage therapy for the time being.

A nice break sounds in order!

Oww, I'm very sorry to hear that. You should do a search for shoulder stretches and give one of those a try. Maybe you don't have enough back support while you're sitting.

Take your time to recover!

Take as many breaks as you can between commissions. Don't overdo it.

I read a similar journal from a dA artist a long time ago who worked himself so hard he gave himself permanent back problems. I thought it was this guy http://steve-huge.deviantart.com/ but it was maybe two years ago and I can't find the journal.

Anyhow, you're workin to hard if you know your shoulder is aching because of art, so go do some excersizes to loosen it up, do some shoulder rolls and stretches and then maybe some pushups and stuff. Almost any chest & shoulder workout routines will do you some good if it's just knotted up.

Take care of yourself.

well, you take too many commissions from Zaruchen it seems, that's what you need a break from XD

and good workouts for shoulders to loosen up tensions would be like moving your arm in circular motions. And for the workouts I'd say push ups (yes they work out the shoulders too), shoulder raises with lighter dumbbells and maybe some stretching too. It always depens on what you exactly want, if you want to built up muscles, loosen them up or similar things. Building up those muscles would relax the joints in your shoulder if you have problems with them too. ^^