It's been a while back, but some people here posted that the new thing now is to prescribe anti-depressants (I don't know which type) to people with IBS because it somehow regulates the intestinal tract (provided your IBS is caused by functional issues, not, say, bacterial overgrowth or parasites). They know that stress doesn't cause IBS, but it can make it worse. They also believe that the intestinal tract is not regulated by the brain, but by it's own semi-independent nervous system (or something to that affect), which is why it's so hard to treat. The anti-depressants, though, help un-depress the intestinal brain and make them work better. it actually has nothing to do with a person actually being depressed or even stressed. Sort of an off-label use, really.
You might want to do some research into the connection between anti-depressants and IBS and see if you can't find out which ones seem to help people with IBS (not all of them do) and see if you can't try some. It may or may not help your actual depression, but if it helps your IBS, then that's one less thing to stress you out, right?