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Sometimes urine pregnancy test can show negative results even though you are pregnant. This happens due less concentration of pregnancy hormone (HCG) in urine during early pregnancy. Your symptoms (nausea, mood swings, increased sweating, heartburn) suggest that you could be pregnant.
I would recommend you to get examination done by your gynecologist and get a blood beta HCG test along with ultrasound scan done to confirm/rule out pregnancy. You can also take a repeat UPT (urine pregnancy test) after 10 days. If the tests come out negative, consider getting started on antacids to combat gastritis and maintain a well balanced diet.
Take care.