I have tried Milk of Magnesia and it didn't work at all for me. Now I am trying Natural Calm (by which so many people here are swearing) and we shall see how this works, cause otherwise I am on Miralax (a prescription laxative) and don't want to be on it all my life.
My simptoms were pretty much like yours, however the Miralax helps only with the C I think, gas was still there until I discovered beano (thanks to this board!). Beano doesn't take care of ALL the gas, however it generally reduces its quantity greatly (I mean it only works for beans, and several other things, right?).
If you are lactose intollerant, are you eating any milk or other dairy products? Because that's how lactose intollerance manifests itself -- with lots and lots of gas. You can try eliminating dairy and see what happens. Eliminating dairy is a magor part of the diet this board is all about -- it's Heather's Eating for IBS diet. Are you familiar with that? If not, just look around the site www.helpforibs.com (not the message boards, rather the site itself) and you might find that it's what you are eating that is causing your problems.