My IBS comes with pain in my lower left side, crampy diarrhea, constipation (amazing how you can get both, huh?), and gas. What a combo. Sometimes I also get a feeling of incomplete evacuation, and leakage after a BM (WAY TMI, but hey, that's what these boards are for, right?)
I worried mine was more sinister as well. But I got a complete work up done, with colonoscopy, and sure enough its the IBS my primary care told me it was to start with.