I Am A 69 Year Old Female In Fair Shape.

I am a 69 year old female in fair shape. Lately my muscles started shaking after I've been sitting, for any amount of time, or laying down. It's as if my muscles are having a hard time supporting me. I'm slightly obese and on different types of meds, including pain and depression meds. Do you have any idea why this has started? I've been the same weight for years and have taken the same meds for years.