constant feeling that my leg is about to cramp?

For about the past 2 weeks I have have had the persistent tight feeling in both of my legs (and the sides of my feet) like they are about to cramp up (like when you get a charlie horse). I didn't do any rigorous exercise at the time or recall anything unusual that may have caused it. Walking or moving my legs seems to help but when I am sitting still or trying to sleep, I can feel it. It is very uncomfortable, and almost pulsing sometimes. When I was little, I would get very bad leg cramps at night that would prevent me from walking for several hours and felt worse than breaking a bone, so the constant feeling like that is about to happen, although it hasn't actually happened, is very scary. I'm 22, so I really don't know what it could be, but it is really affecting my sleep because I keep waking up and having to walk for a few minutes before I can fall back asleep. If you have any suggestions of what it might be or how I could stop it, I would really appreciate it!