Kathie, There are researchers still uncovering more MG antibodies! Though there are not tests available yet. So, yes, you can still have MG and be seronegative. Did your MuSK test come back already?
Have they done a CPK (creatine phosphokinase)blood test on you? Could polymyositis be a possibility?
http://www.mayoclinic.com/health/pol...-and-diagnosis
I've done as much research as I can at the moment and cannot find a reason why Indomethacin could make MG better. It would make any "itis" (meaning inflammation) better.
It might be worth a 2nd opinion by a rheumatologist. Sometimes it helps to have an other specialty have a look see at your symptoms/test results.
It's frustrating to not know what's going on. I hope you can get answers fairly soon. Take it easy in the meantime!
Annie