Hello,
I have gone through your query and understand your concern.
No. Pregnancy is not possible.
As you have taken the
Oral contraceptive pills and also had withdrawal bleeding after 3 days of stopping the drug.
The cause for your
abdominal pain and back ache could be some thing else including gastritis.
Sometimes foods you eat that cause abdominal pain can lead to gas pain that seems to radiate to your back.
It may also be caused by Gall stones, kidney stones,
ovarian cyst,
urinary tract infection (UTI), tumors, such as an
ovarian tumor.
You need the physician help for simple physical examination.
He may ask detailed history of the abdominal and back pain and associated symptoms like blood in your stool, vomiting, blood in your urine, headache, heartburn etc.
Based on the findings and clinical diagnosis, he may recommend any further investigations or he may treat with some antibiotics if he suspects any infectious origin.
Hope this helps.
Please write back for further queries.
Wishing you good health.