What causes ulcers

I am 4 mos. Post Op gastric bypass and just found out I have a huge ulcer that takes up 3/4ths of my new pouch. How did it form and why? Did I do something wrong in my diet? I need answers.

We greatly appreciate your interest in helping us build our Q&A database. To discourage vandals from posting garbage, however, we require people to register before posting.