gastritis causes??

I recently had a gastroscopy that revealed that I have inflammation in my lower esophagus and stomach. My doctor did take a couple of biopsies, but the results are not back yet. I was prescribed omeprazole for a relatively short time period (4-6 months) in order to allow the affected tissues to heal.
I cannot figure anything that I have been doing that would cause this condition. The only thing I do that could possibly contribute is alcohol consumption, but I only drink and average of zero to maybe 7 or 8 drinks per week. Could this moderate amount cause inflammation like this? I don't generally eat a lot of acidic or spicy foods either, and the only time I take NSAIDS is the first day or two of my period.

My doctor ultimately wants me to control this through dietary changes, so I'm trying to figure out what I can change.

Oh, also, I had almost no pain/symptoms associated with this; if it wasn't picked up on the gastroscopy I wouldn't have even known...

Advice?