I've been fighting this for years. There were only two things that would help me - getting up and walking around, or else laying on the bed on my tummy so that my feet would dangle off the edge. That would force my legs to straighten out and make it go away. Unfortunately that second one doesn't work so well with a baby bump.
I have a hematologist for a separate blood issue, and he asked me if I have restless legs. I told him yes, how did you know? He said my iron is very low and put me on iron suppliments. He told me it takes 90 or so days to take effect, unfortunately, but it did work after about three months and I don't really have it anymore.