The chronic sinus and allergy symptoms you mention lead me to believe the underlying cause for your IBS symptoms could be fungus related. The Mayo Clinic has even said that chronic sinusitis is caused by fungus. GERD, acid reflux...again, fungus has been implicated. You probably have been taking antibiotics at some point in your life...recently even? They are by nature, fungal toxins (poisons) and cause a myriad of disease and ill-health problems. Perhaps antifungals would help you. Would your doc prescribe diflucan for systemic fungal overgrowth, or even nystatin for gut overgrowth? Natural antifungals have helped me, like olive leaf extract, caprylic acid.
I also need to stay away from any foods with yeast/yeast extract listed in the ingredients. Causes D and bloating big time, especially if I have been eating a lot of higher /sugar foods, as well. Think about yeast rising in bread. What causes bread to rise? More info you can read, that helped me, can be found on www.knowthecause.com. Click Resources tab at the top, then on next page- Resource Categories on left sidebar- look under FAQ's. There are 3 pages there you can read about the phase one diet, and other info about fungus. Actually, browse the website and learn a bit more about fungus. I never actually thought I had a fungal problem until I experimented with the diet and felt so much better. If you do have a yeast/fungus overgrowth, only a low carb diet will help, along with antifungals. I also recommend probiotics.