I have had IBS/A lazy bowel since I was 3 years old - I am now almost 51. Stress does play a big part in it, I never suffer from Constipation im the opposite and always get the runs. I know when I have a bout coming on, I get unbearable pains in my lower abdomen, and start sweating really badly. Its the muscles going into spasm in my stomach.
Its trial and error with the foods people eat, I find with me its mayonnaise (as it has raw egg in it), red cabbage, salted nuts, too much chicken, some fruits. Ive found since starting SW its not half as bad and I think this is because I now make 99% of my meals from scratch with fresh ingredients.
As mentioned it may be worth keeping a diary and trying to eliminate the foods which trigger it. The doctor can prescribe colpermin which is peppermint based as this settles the tummy ( peppermint drink can have the same effect) , Buscopan is another drug. None of these worked for me, now when I have it really bad or can feel the spasm coming on I have to take immodiums and they help, but the doc stopped giving me these I have to buy them now