What Causes Leg Muscles To Cramp And How To Treat It?

I keep getting severe muscle cramps in my left leg - this started around a month ago, an mainly when I'm in bed. Recently they've occurrred when I've been walking during the day. I had to have an operation on my torn Achilles Tebdon around 8 months ago, and it wasn't entirely successful - I can't bear my weight on that leg? Could this be the reason for the cramps? My family want me to see the doctor, but it seems such a minor thing.