I'm really sorry to hear that KnittenKitten. But, I'm glad it's something treatable and the meds might help both conditions. Guess we have to find the good in it.....however small it may be.
You definitely deserve to vent. And gripe and whine. And get angry. Let your family help you in any way they can. It makes them feel like they've got some control over it, too. Sometimes it's nice to be taken care of....even if it's just for a little while.
I hope you find the right dose of steroids and it helps both the MS and the polymyositis.