Jello contains adipic and fumaric acid they put in there for tartness. There is probably not a lot in there, but people with ulcers need to be careful. Otherwise, the rest of the ingredients are sugar, disodium phosphate and the jello
Jello is great for after you have had the flu and do not have the strength to digest a whole meal yet. Chicken noodle soup, crackers, Jello, ice cream and Coke or 7-up for those folks.
But for ulcer people, might want to stay away.
PS, do not eat red food color before any testing for ulcers. It can be mistaken for blood, and can make negative tests look positive.
And please see a doctor ASAP. Ulcers can bleed and get way worse, and there are other things that could cause problems.