I have been troubled by a weakness in my right side ( I am completely left-handed, left-footed, etc). Last year I had an ankle problem that required surgery. I came back from that and ran happily for 2 to 3 months until I began to get pain on the lower right side of my right knee. I was ok until I ran downhill but after that the pain didn't go away. I stopped running for about 6 or 7 weeks (I did no exercising at all) and then started running again and the knee was fine. Over Christmas I developed the same problem and now each time I run more than about 15 minutes I suffer a lot of pain. The following day walking downstairs is painful but walking upstairs or on the falt is no problem.