Me too. My knees are weak too. Did you ever get an answer from your doctor? Pain could be from arthritis, especially if your knees are stiff and sore. You should get an x-ray. Let me know what the doctor says. You should also get an EMG for the nerves to your knees! Some of my EMG nerve study tests were abnormal, (but they were for the nerves to my toes. Why did they test my toes?) My knees are weak, also. The rheumatologist said the cartilege under my kneecaps is "softening" and my kneecaps are "unstable" and she moved them back and forth with her hands. Perhaps your knees have cartilege danmage. But, since my leg muscles are SO HEAVY AND STIFF and hard to move when I try to get out of the tub, I know something else is wrong! I can not climb steps or get up from the floor, either. Lets try to help each other!
Get your renal function and lipid profile checked. I don't know if you are still watching this but I will research what I can.
Me