It has been suggested that perhaps you're not tired enough when you go to bed; my problem is usually just the opposite if I can't sleep...I'm overtired! You know how children get when they get overtired? Can't seem to wind down? Same goes for grownups.
I didn't see your age, so I don't know if you're a teacher or a student, old or young. However, if you were born before the polio vaccine came out, is it possible that you had a case of polio? Even if it was so minor at the time; even if it was to the point where you were sick for a brief period of time but then, seemingly "got over it" and went on with your life? Many of us who did have polio when it was of epidemic proportions in the US are now experiencing what is called Post-Polio Syndrome. I'll not go into all the symptoms here; however, pain in the lower limbs and/or back is one of the first and longest-lasting symptoms.
Otherwise, I agree with the person who suggested possible MS (Multiple-Sclerosis). I have several friends who have MS and leg pain, numbness, etc. are pronounced symptoms of that. However, it's an ardent foe when it comes to diagnosis so be prepared for a long, involved process if you wish to be tested for it. Hope my thoughts have been helpful.
Oh - one other thing. Have you considered asking your doctor about a sleeping aid (pill)? There are several new ones that are excellent and as long as you commit to getting 8-10 hours sleep, there is no "hangover" like what the old sleeping pills used to cause. They were usually valium which is also highly addictive. These new aids aren't AS addictive as valium, but one can become dependent on them so they suggest that they not be used long-term.