Would chronic gastritis give you intolerance to wheat/celiac. Or other way round, could wheat/celiac sustain gastritis?

Celiac can upset. the stomach and the feeling it would give could be similar to gastritis. Gastritis cannot cause Celiac disease.
Yes. To both. It is more likley that wheat intolerance lads to the gastritis. The biggest reason is that so much of our wheat is genetically engineered and studies are showing it wreaks havoc on the intestinal system. Stop gluten and see if your symptom improve. If not, then see your doctor.