Lialda (mesalamine) does have the potential side effect of gas, among other things. I really notice it myself when I do mesalamine enemas. WOW do I get a lot of gas! The oral meds don't cause quite as much, but I'm pretty clear they're responsible for the gas I do have -- not as bad as what you describe but more than I want, for sure.
As soon as you get over your reluctance to consider rectal meds, I'm sure you'll thank yourself. My anus is really sore from overuse, and there are nights that I think, ohhh, I really don't want to stick anything UP there, either because I'm in a calm moment and I don't want to stir things up or because I'm in a bad moment and I don't want to make things worse, but I do it anyway and I am always glad I did. One reason I tend to credit the enemas with my improvement is that the first time I used corticosteroid enemas, during my last flare, was also the first time I had a solid-ish stool during that flare. I really do think they make a huge difference.
This is kind of silly advice, but when babies have a lot of gas on their tummies, you put them down on their backs and "bicycle" their legs to get it to move out. I do that myself, alone in my home, either on the carpet or the bed, if I feel bloated and like I need to get a lot of gas out. It shuffles things around, relieves the pain, and gets it out for the moment.
Good luck