It has been known for many years that statins can cause muscle pain in anybody, not just those with myasthenia gravis. Some of the statin drugs are worse than others.
In my case, extremely high, heredity -caused high cholesterol has to be controlled by medication, a controlled diet did nothing.
Do you see s cardiologist? If not, maybe meet with one to find other statins that are known not to have as many side effects?

I take Atorvastatin. Most of my pain is joint pain, caused by degeneration.

Lisa