Weak leg is becoming a bigger problem

I've been having trouble with my rt leg just going out from under me at times. This seems to come from nowhere and just sneak up on me. Also mussel cramps in the same leg have gotten worse. My tremors are very minimal now thanks to Sinemet, but so far I have found nothing that helps with the weakness and cramping of my leg. 
Exorcise for me has to be limited do to heart issues, but I do try to walk on a treadmill for 10-15 minutes at a time when I feel up to it. 
Anyone else have this problem?  I really don't want to complain, because I know things could be much worse, but it's becoming a big problem for me.
 
Thanks for any input