Becky, been there done that. I suffer from IBS, and have just hit my 3 stone aim. Exercise is perfect. You would be surprised at how beneficial it actually is and how much difference it makes. But it is worthless without a good diet. My first week was a bit hard, not only emotionally adjusting to the new routine but also the body kind of calibrating itself with everything that's happening. So it can get worse before it gets better. But after a week it settled and I tell you what I never looked back. Most of IBS is stress related and exercise is brilliant at combating stress, depression and anxiety. You are on a right path. But whatever you do don't go on those stupid diets that cuts out certain foods full stop.
Learn to combine your foods right, eat healthy small portions, plenty of fruits, veg, and don't forget water. Cut down on caffeine, booze, dairy, fried, and extra spicy stuff. And stick to the exercise.
All the best. S.