I Have Been Having Weakness In My Legs And Arms

I have been having weakness in my legs and arms since my triple bypass surgery in 2013. Three weeks ago, my legs have become so weak that I feel my hips cannot hold the weight. I have to walk slow because often times I lose my balance. I have done all blood work, thyroid function is good, Ac 5.7 no vitamin B C, or deficiency. .. What else could it be