I've been having mild stomach discomfort for 4 days now. no vomiting or diarrhea, can eat, so just a persistent stomach bug? or acid?

Many causes: If it persists another few days, you should see a doctor. It could be something simple like a virus or stress or more complicated as there are many organs like liver, pancreas, spleen, etc, in the area. If you are still going to the bathroom regularly and appetite is good, then you can probably wait a few more days to see a doctor.