I fully agree with 4-eyes, you are definitely not properly medicated. You didn't tell that you were taking 20 mg/d Pred, when did you start this? Did your condition worsened with Pred? If yes, this is quite common but your dosage will probably be increased to 1 mg/kg of your weight. The early stages of your MG are the same as mine and it took about 1 to 2 months at 50 mg Pred for the double vision to disappear. Limb weakness (I had trouble brushing my teeth...) stayed much longer despite Cellcept, IVIG and only Plex with Mestinon (6x60 mg + 1 timespan) were effective.
Curiousy my early weakness was in the arms, the legs were OK but after 6 months, the weakness switched to my legs and the arms gradually improved. Laying flat is usually very difficult (saliva swallowing...) and I was sleeping half sit.
Again, with 4-eyes, avoid gym...
Maurice.