I have lower backaches and legs that ache also but it is not MG related. I have stenosis in my L4 and L5 vertebrae. I also causes sciatica (shooting pains), something that happens to me. It also causes weakness in legs.

Stenosis amplifies the weakness caused by MG because it also causes weakness from your hips down.

I hope there is a simpler explanation for your situation for your pain and you find it soon and something can be done about it.

scrubbs