Hi,
Welcome to the forum. I am really glad to help you out. The possibility of pregnancy needs to be ruled out. To confirm the status of pregnancy, I would suggest you to get your serum HCG levels estimated since this is more specific than urine for pregnancy tests.
The HCG (it is a hormone) levels rise only in pregnancy and its presence will confirm the status of your pregnancy. Moreover, the HCG levels are raised around 10 days after the implantation of the zygote. Meanwhile, you can take some drugs like gelusil MPS & omeprazole/pantoprazole to take care of the gastritis. I sincerely hope that helps. Take care.