My abdomen has hurt for a month. Gets worse when I eat or drink anything. I have been treated for gastritis & told maybe I was just constipated ideas?

Examination. Abdominal discomfort lasting a month calls for an evaluation by your physician. Conditions such as gastritis, peptic ulcer, liver or gall bladder problems, inflammation of the intestinal tract are some possibilities.
Need to see doctor. Abdominal pain for a month is not normal. The only way this can be evaluated is in person with a physician who can examine/palpate your abdomen. Plus s/he need to see if it's soft, hard, cold, tender, lumpy, or painful in all quadrants including the center by the umbilicus. So don't delay! This is very important. This is somewhat impossible to do virtually as different organs lie in close proximity.