I have upper stomach pain, constant nausea, sour burps, constant discomfort. I think it's gastritis. What can I do to feel better?

See your doctor. Upper abd symptoms can be many cause. Stomach ulcer, acid reflux, gallbladder, irritable bowel syndrome. See your doctor for proper DX and treatment.
Reflux... The sour burps tell me that stomach contents are probably going up the esophagus. This will also cause discomfort and nausea. First eliminate things that can cause reflux - caffeine, tobacco, alcohol, teas, acidic fruit. You probably also need a medication to decrease the acid in the stomach, otc meds include Prilosec and Prevacid (lansoprazole) (they don't work immediately though). Check w/ your doc first!