hip and leg muscle pain

i was diagnosed with myasthenia gravis about a year ago and was put on a treatment of a commonly used steriod and mestinon. well the steriods made me feel weird and after the initial prescription was used up i never refilled it and only used the mestinon. using the mestinon helped immensly and i didnt see any adverse affects on stopping the steriods. anyway about 2 months ago i started feeling a sensation in my left leg, as if i strained a muscle or gland. the sensation developed into hip and leg pain the strangle subsided in one leg then switched to the other. i went to a local doctor who after chatting for a few minutes said it was inflamation in the joints (i had a mild flu a week before the symptoms) and put me on an anti inflamatory. well no improvement , rather more pain less mobility, so fustrated i went back to the expensive specialist that diagnosed the initial myasthenia. he was aghast that i stopped the steriods and suggested the the joint and leg pain was a result of the myasthenia. i did some web research but it dosent seem to add up i cant find those symptoms associated with myasthenia. could stopping the steriods have caused this? even though i have been great for the past year