After 16 yrs on depoprovera i'm about 2 have 2nd cycle. i do have myasthenia gravis. is it "normal" to get really tired and weak feeling wk b4 period?

Most do not: Most women do not complain of fatigue and weakness each month before each menstrual cycle. Some who suffer from PMS/PMDD do complain about such things. You can monitor your cycles over the next few months and see if there is a pattern for you. If you feel you are having a myasthenia flare then see your Neurologist sooner rather than later.