Good for you for gettin' goin'! Actually, I believe exercise is one of the best things you can do to alleviate symptoms of IBS. I personally think that anyone who is chronically unwell in some way should place themselves on a regular exercise schedule. When I become a doc that is going to be one of my major goals, to get people exercising more. At least half an hour of exercise each day is recommended. If you had a good run, maybe you should think about signing up for a local 5-K race; it's a good distance for beginner runners!
I used to read "Runner's World" magazine like it was my job, and it really helped to motivate me during all my years of cross-country running and half-marathon training. I'm actually thinking about doing my third half-marathon this summer before I move to Arizona.
Sarita, I'm not sure that running is good for everyone. While exercise, in general, is necessary, some people are just too sick for running. In their case, walking would be the best exercise. I know people who have reflux who were told not to lift certain weights since they can burst open a certain valve.
Running can be bad for people who have palpitations/heart problems. But walking seems to be good for everyone.
Running is definitely not for everyone; for some people, it's hard on their joints, and it does tend to cause injuries if it is not approached properly. Walking on a soft track, trail, or treadmill is also a good choice.
However, running or other intense aerobic activity may actually help people with heart palpitations. Increasing the heart rate affects electrical conductivity, and sometimes can sort of "re-set" the heart. I remember when I was having a particularly nasty bout of PVCs (pre-ventricular contractions) in college - several hundred over the course of a few hours - the on-call physician I contacted told me to take a brisk run around the block a couple of times. It was uncomfortable at first, but the palpitations vanished when I got my heart rate up to a solid 160 or so. However, people need to make sure that their palpitations are benign before they start slamming themselves with the intense aerobics :)