Lately My Lower Body Has Been Very Weak. It Started

Lately my lower body has been very weak. It started in my right thigh, and has moved to my buttocks. I am basically experiencing a general weakness with some pain. It is not nerve pain but more like muscle fatigue. I am having trouble walking up and down stairs. I am 69, but am moderately active, play golf 4 times a wek (use cart though). I do have diabetes and have to use insulin shots. My legs have always been strong. I get enough sleep. Eat reasonably well. Any comments?