Hi Sylv,
I feel for you! Leg cramps can be miserable! I don't have them but I do have alot of jittery, shaking with my legs at night, especially when I'm trying to sleep.
I think Erin may be right about the Ferritin. My mom used to have horrible leg cramps due to a blood disorder and I know the Dr. talked about her ferritin levels. Her Dr. had her take something over the counter called Quinine. My youngest son also took it after he was involved in an ATV accident and had alot of trouble with his legs cramping. Please check with your Dr. or your pharmacist before taking it to make sure it is safe for people with MG. I am a newbie myself and still have to check on everything before I take it.
Hope you can get some relief soon!