"Very focused" sounds more like an ulcer. I think gastritis can be "focused," not sure about "very."
For a feeling of "burning" and "gnawing" I would say the top three things to look at would be ulcer, gastritis, and acid reflux. But I'm just a layman.
Try to be very mindful and notice if any foods make it feel better or worse. For example, if consuming vinegar makes it much worse, that makes ulcer or gastritis more likely. If known heartburn triggers like caffeine make it worse, that points to acid reflux.