Neither foods or stress cause IBS, but both contribute to generating the symptoms.
" The fact is, I get it when I'm really relaxed"
Stress has a delayed reaction. Nor is this the kind of stress you thinking about.
IBS is consider a chronic condition and there is not a cure. There are effective ways to manage the condition however for most people.
Its important to understand the connections to stress and depression and IBS as much as it is understanding foods and IBS, even the act of eating.
A good doctor will be able to tell the difference between IBS and gallbladder problems.
You should read over this sites carefully.