It might be a good idea to go into the gastro forum on this site to get an idea of what others are experiencing. I'm not sure if one has anything to do with the other. Good luck.
But please can you tell me why the diseases are interrelated. Which one in your opinion, is provoking the other?
For the sinusitis-try going to GNC and buy a spray called sinufix-works great-if a possibility of allergy to herbs, check before use. As for the stomach-I would go to gastroenterologist to request an endoscopy to actually see whats going on from the throat to stomach; if not, ask for a script for coating the stomach before any foods/drinks are induced. Along with this, I would ask for a script- nexium or prevacid or whatever your physician may want to prescribe. This should help. Try it you have nothing to lose. As for the migraines, maybe its sinus headaches your suffering from instead of migraines?