Thanks for asking.
Based on your query, my opinion is as follows.
1. Yes, the ibuprofen
taken could have initiated acute gastritis
2. Gastritis will induce abdominal pain
, which will be on and off varying with food.
3. You need to start on antacids. Later proton pump
inhibitors or H2 blockers can be used.
Hope it helps.
Any further queries, happy to help again.