Hi, Motorcycle Diva. Welcome to the forum! Did you know that your initials are MD, as in doctor?!

Do you have an informal name we can call you by?
Sometimes people can get a steroid myopathy. Steroids can also cause numerous vitamin deficiencies, like Vit. D. B12, calcium, albumin and iron. Have you been tested for any vitamin levels? I think you should bring this up to your primary doctor. Steroids are antiprostaglandins. What they do is reduce the gel coating of the stomach and can reduce the amount of stomach acid. We need stomach acid to properly digest our foods so that by the time it gets to our small intestine, where nutrients are absorbed, it is broken down enough for those nutrients to be absorbed.
Do you have insurance? I know Mestinon is high. I'm not sure if they have any programs for it or not.
I take Mestinon and coffee.

Caffeine is a cholinesterase inhibitor like Mestinon is. So are the nightshade foods (tomato, potato, eggplant, peppers, tobacco). There's just something about coffee, besides the dopamine in it, that helps give my MG that extra boost in the afternoon.
I hope you can figure out why you are having such pain.
Annie