Hmmm - are you getting fiber and protein at every meal? While eating starchy and sweet stuff is IBS safe, it's not very filling and satisfying by itself. Something like vegetable soup might be a good addition to the lunch you listed - low in calories, but a lot of volume and nutrition and safe IF.
Plus, I'm always extra-hungry in the fall. Don't know if you're wired like I am, but less sun plus cold weather makes me *starved*! Did you feel this hungry in the summer?
I would definitely go to your doctor and ask about testing for parasites if this goes on for very long. For the moment, concentrating on protein and fiber and reducing the amount of sugary stuff in your diet might help prevent that crashing feeling.