Hi,
Welcome to the ehealthforum and I am glad to help you out. If your last menstrual period was on 15th june (as given in history) and you have missed the periods of July then chances of pregnancy cannot be denied.
Pregnancy definitely needs to be ruled out and for the same, urine for pregnancy test can be repeated and in case it comes out as negative, a serum beta HCG pregnancy test can be carried out. This is a much more sensitive test than the urine test.
If pregnancy is ruled out then gastritis and gastrointestinal infections should be evaluated.
I sincerely hope that helps. Take care.