Ezz totally said what I was going to say
I find if I wake up, have a stretch and point my toes I start to feel the burn so I then stretch my calf and point my toes up... lukcy enough if stops it in its tracks!

And with the salt try using the iodised salt and any natural fruits ect that contain lots of magnesium

One thing I can confirm is they stop pretty much the moment baby arrives!! :P doesnt help you now I know but something to look forward too!!

Good luck and hang in there
xoxoxooxoxox