I get the same thing. I have tendonitis in my left elbow and after a long class my elbows are very fatigued and it makes my whole arm weak. It would get so sore that i would be unable to fully straighten my arms when doing stuff at the gym like chest and tricep stuff.
I had acupuncture done on it at this Chinese medicine place a few months ago and the pain went away completely for a few weeks. It has since come back, but it's not nearly as bad as it used to be. Maybe have a look into doing that, it was only $30 for me - well worth it. The acupuncture doesn't hurt or anything.