What Causes Numbness And Weakness In The Legs?

I have been on kidney dialysis for over 1 year (Pertenesis)..about 2 months ago my legs got a red rash on them and I my legs started to get weaker and weaker. The red rash went away but in that area it feels kinda of numb and my legs have gotten weaker. I can't run or go up stairs without needing some assistance. My doctor doesn't know if its the high potassium that I have or my red blood cell count is low and I have been taking more epogen (shot). Can you tell me what I need to do?