Dear user, welcome to healthcare magic. There are two possible explanations for the gastritis during menstruation. The first possibility is that there is preexisting gastritis, which is aggravated during menstruation due to the accompanying stress. The other possibility (far more remote) is the presence of a rare form of endometriosis in the gastrointestinal tract. This is a very rare possibility. As long as the condition is severe and persistent I suggest having an upper gastrointestinal endoscope during the attack. I think this will be very helpfull if your doctor agrees. I hope these words were useful to you. Good luck. Dr. Ahmed Bahaa.