Vomiting spells

For the past few months, Shelby has been having regular vomiting spells that occur every 7-10 days. At first we chalked it up to her constant mouthing of toys and figured she was just catching every stomach bug in sight. But then it kept happening. At the beginning of April, I was sure her shunt was slowly failing (vomiting and lethargy are the main signs of a shunt malfunction). But we had a scheduled MRI and check-up with Dr. Grant at Duke over spring break and he said everything looked fine. This was a huge relief...but then the vomiting has occurred four times since Spring Break and we are stumped. Shelby's eating has advanced and she is tolerating larger bites and more textures of food, but I wonder if she is chewing thoroughly enough. Could her stomach be upset from that? Our pediatrician thought Shelby might have reflux and prescribed Prevacid. The neurologist thinks Shelby might be experiencing migraines (especially considering that Trip gets them). Another person suggested the glasses might be giving her headaches and someone else thought Shelby might be having a food allergy. We are now keeping a detailed log of everything she eats. Whatever is going on really stinks (she is missing school and feeling bad, we are losing sleep and missing work). We've got to figure this out!