Maybe it is from something other than aspartame. Though it could be you are exposed to some form of hidden aspartame, or are overlooking a product you don't think of as being sugarless (like most Sugar
gums now contain Aspartame
as well as sugar). Some health products like drink and protein powders, or vitamins contain hidden Aspartame
which they do not list on the label. Look for this warning "attention Phenylketonurics: contains Phenylalanine." If you find that on a label, it's got unlisted aspartame.
Another thing that is said to help alleviate restless leg syndrome is Magnesium Citrate. See: http://www.allcalm.com/restlesslegs.html
I hope you find an answer and get better soon.