Headache can be due to numerous reasons like migraine,unresolved sinus infection, allergies, inner ear infection or defect etc...based on history given by you it might be due to migraine with additional headache due to gastritis... I would suggest you to consult nearest neuro physician and try eating several small meals instead of three large ones whenever you can...Avoid foods that irritate your stomach, especially those that are spicy, acidic, fried or fatty... avoid coffee,tea etc... Avoid Stress as it may make your gastritis symptoms worse...consider calming activities, such as meditation, yoga etc...sleep with head raised position and have dinner at least 2 hours before sleep..take over the counter medications with above..consult physician if symptoms persists.