Hi Scarlett,
I used to put on a few pounds in weight a few days before I was due, due (lol) to water retention. GP prescribed some diuretic tabs for me to take about a week before - certainly helped - but never comfortable (Mr Blobby) for a few days after the onset. S'pose we are all different though, like some lucky s*ds don't suffer much with the monthly miseries. Go see your GP for some tabs. You can of course buy them in chemists and health shops (whether they are 'industrial' strength, I don't know), but sometimes non-prescription meds are cheaper over the counter - check with the doctor - they should tell you if you are better off purchasing them from shop, rather than by prescription.