I have had similar problems, to the point I contemplated not taking them anymore. I asked for the slow release right from the start as I also suffer from IBS. I built up slowly, over the course of a month, to 2000 mg. I can honestly say it took me at least 4 months to get used to Metformin. Strangely enough, I did NOT have any gas at all. I *wish* I had, as it all built up in my stomach and it looked like I was 9 months pregnant. However, I had chronic diarrhea for the first 2 months. It was a hellish cycle of either being blown up like a balloon, or being on the toilet most of the day. I resorted to taking a lot of anti-diarrheals if I wanted to leave the house at all. I also had a very hard time eating, no appetite - but if I didn't eat with my meds, I felt much worse.
As the other posters suggested, ask for the slow release. If you have built up gradually, you may want to ask your doctor about cutting back and building back up again. Try to eat lightly, low-carb and drink PLENTY of water with the pills (before and after you take them). Take them in the middle of your meals and see if that helps. Good luck. I feel for you! I know its hellish getting used to them!