What Causes Muscle Weakness At The Back Of Leg And Hip?

I have muscle weakness in the back of my right leg and hip and on the outside of the hip. My leg has slow response. If I go over 3.5 mph, on the treadmill, my toe will occasionally drag. When walking my foot seems to stay flat rather than bend and rock on the toe. I have taken cholesterol medicine for a few years, but this condition started last fall and has gotton worse. Thank you for your time.