Mummyof2tob...

Lack of Magnesium is probably why you are getting the cramps - Rennie which are similar to mylanta contain magnesium, which is why they work too.
Dont increase salt in your diet as this will only make the cramps worse.

My sister is a footy trainer and when the guys come of the field they get a rub down with a magnesium cream and also a leture about dehydration as this also contributes.

Try thinking back to the days that you get the cramos the worse, are you doing more physical excercise (ie loosing more fluid), not drinking enough or eating a particulay salty meal?

I find that stretching before bed (i have not git a cramp since increasing my fluid intake and using a heart burn relief) also helps. Make sure you are drinking enough H2O during the day

HTH

ETA: when you get a cramp - get out of bed and walk around and stretch it out - very painful, but will reduce what you feel the next day