I am experiencing pain in my left knee. I usually try to run 3 times a week about three miles. Since my pain started three weeks ago, I have stopped running and treated it with ice and Advil. The pain seems to be inside the back of the knee. It does not hurt all the time. There are times when I feel unstable putting my weight on it. The knee does feel better than it did last week but it is still bothering me. In my early 50s and female. What do advise?