Does taking ppi for long time such as pantoprazole, omeprazole causes gastritis?

No: Those are medication to prevent gastritis, if u r still having symptoms it could be u r not uncontrolled with those ppi or it could be more serious like an ulcer, a bleed, an infection, etc. if u haven't seen ur doctor for it, I suggest u do

Depends: If u are taking these medications for years and years they can cause atrophic gastritis. The treatments is different but it involves making sure that your B12 levels are normal, your Folic Acid levels are normal, and to take breaks from the medications.