On and off for the last 3 months I have had strange sensations in my legs. Not weakness really, just the rubbery leg feeling you get when you need to strech your legs. Usually this happens when I first stand up. After walking for a few minutes it goes away. This doesn't happen every time I stand up just every once in a while. I have also been having some weakness behind my knees and in the knee joint along with a little muscle cramps and some pain in my foot. My doctor ran tests for thyroid, rhumtoid arthritis, infection and connective tissue disease and found nothing wrong. My leg endurance is fine. Just last week I was walking 3 miles a day. The doc thinks it is stress, but I don't know about that. I am a 37 year old male with no other health problems. Oh by the way, sometimes after walking my calves really tighten up. And I also get a weak feeling sometimes in the front of my thighs. I have also felt some slight heaviness (weakness) in my upper arms and across my back.

Any thoughts?

thanks