For about 3 months I have had aching legs, almost constantly. Sometimes it keeps me awake at night and it there when I get up in the morning. Mainly the back upper part of my left leg but they both ache. Its hard to find a comfortable position, either sitting or standing and standing seems to be worse. What could be causing it. I am 64 yrs old, am female, 5'4" and weigh 150 lbs. I have always been healthy, never been in hospital except for childbirth 3 times. When younger I walked and exercised a lot but not so much in the last few years and now that I have so much pain, I don't dare go for a walk. What could be causing it? don't know if its muscle, nerve or bone pain.