I am on week 5 and I had a few in my legs in the middle of the night last week, but apart from that I haven't suffered. I always thought cramps were to do with circulation. Sorry I cant help hun.
What ya are getting is a side effect of a vlcd which are muscle cramps and nothing to be worried about. They normally last for about a couple of weeks as your body goes into a shock mode and gets used to the diet. They are probably more annoying to yourself but wont affect ya on the diet.
Some people tend to be different, there are some other side effects as well but i think most people just tend to look on the bright side of things of losing the weight and bear with it but they can be very annoying
I know you can drink sparkling water, but I dont know about the other 2. I would think tonic water is a no, but soda water might be a yes, but dont take my word for it, wait for someone who knows.