They are numerous reasons for a woman of reproductive age to have a missed or delayed period the major one being pregnancy. Home pregnancy test are not 100% effective especially when done too early. So you could redo the test after like 1 week and right now, you could go to the hospital so that direct testing of your blood for elevated beta HCG can be done and if possible pelvic ultrasound
to visual if gestational sac
Other causes of missed period could be stress, weight changes, change of diet or poor diet, hormonal imbalance, uterine scarring, thyroid problems etc.
If pregnancy is not the reason, then one of the above can be and should be investigated one after the other by your gynobs.
Your stomach problems could be as a result of dyspepsia
which could be functional disorder
that requires you readjusting your feeding and probably be placed on medication that regulate intestinal transits. This could be related to pregnancy.
Hope this helps