There's a poster here who's in a very similar boat to you - she might post. Unfortunately she hasn't been able to find a solution to her post-surgery IBS woes :-/
Have you been checked out for SIBO, aka small intestine bacterial overgrowth? If not, then I would, because antibiotics can help with that. Otherwise, you're stuck with the catch-all diagnosis of IBS, for which there is no real help so it seems. If you're interested in tinkering with your diet, there's a couple of diets you could try. One is the low-FODMAP diet. The other is an elimination diet followed by a slow reintroduction of solid foods. Google for more info.
Dx Crohn's in June 2000. (Yay )
Tried: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, diets.
1st surgery 20/2/13 - subtotal colectomy with end ileostomy.
2nd surgery 10/7/15 - ileorectal anastomosis. Stoma reversed and ileum connected to the rectum.
Current status: Chronic flare. Do I have any other kind?
Current meds: 50mg 6MP; Entyvio (started 3/11/16)