Your symptoms looks like Gastritis or could be because of colitis. I don't know what is the composition of the medication you are taking. It could be because of Medication induced.
Next Steps
May be need to consult online Gastroenterologist
Health Tips
1) Avoid non vegetarian and spicy diet for a week or so
2) Avoid pain killer medication
3) Take plenty of water and liquids may be ORSL
4) Take Probiotics (Good bacterial spores) good for your Gut
5) Avoid Smoking and Alcohol consumption (If your are indulged)