More than likely, your bowel troubles are due to your stress. I saw a quote from the Old Testament the other day: 'when God arrives to judge and redeem, Habakkuk is so nervous that his "bowels quaked."' See, even back in the Old Testament, they knew that stress and fear made your bowels go off!
Flu, colds, and other illnesses can definitely get your bowels out of whack, especially if they are sensitive to begin with. Get yourself some yogurt--Activia is getting rave reviews on here--and eat a container twice a day and see if that doesn't help you some.
And yes, a lot of people feel the need to go to the bathroom, but then can't go when they get there. This happens a lot, obviously, with people who have constipation, but I've had what I call the 'dry heaves' before, in which I have emptied my bowels completely, so there's nothing left to come out, but they are still spasaming and moving as if they are wanting to move stool through. So yes, you can get spasms in your bowels that make it feel like you need to go, even when you really don't.