I Have Throbbing Knee Pain At About 3 To 4

I have throbbing knee pain at about 3 to 4 AM in the morning. Once I get up, the pain subsides. If I walk a few steps (e.g. 20), the pain is gone and I go back to sleep. The pain may return 1 to 3 times more before morning. I used to be able to get the pain to stop by simply flexing my knee a few times and then going back to sleep. That method does not seem to work anymore.