Hi ! Good evening. I am Dr Shareef answering your query. Although your stomach problem might not be related to the delay in your periods, I would advise you to go for a serum HCG and an ultrasound abdomen if need be to rule out pregnancy in case you are sexually active. Your stomach problem might be due to some kind of intestinal infection which could come by eating outside which you should avoid if you do. If I were your doctor, I would get your stool test done for ova and cyst, and treat the infection which would relieve you. In case of no relief, I would refer you to a gastro enterologist for a possible endoscopic evaluation of your intestines. I hope this information would help you in discussing with your family physician/treating doctor in further management of your problem. Please do not hesitate to ask in case of any further doubts. Thanks for choosing health care magic to clear doubts on your health problems. I wish you an early recovery. Dr Shareef.