How to tell if you have an ulcer?

For a month and a few weeks i was waking up every morning and puking before or after breakfast. My doc thought it was acid reflux. Told me to take zantac but not quiet. I went to a gastro and he told me to get a endoscopy done but my insurance ran out. I already had bloodwork and MRI done. He said I should get a endoscopy cause it could be an ulcer. The vomiting stopped and hasnt come back for a very long time i had the swine flu a few months ago and now at night when i eat it feels harder to breath? Anyone ever heard of something like this? and how can a ulcer kill me? is there anyway to detect if the ulcer is reaching a lethal stage? and if i even have an ulcer how did i get it? If you ask questions in the answers please recheck for updates and ill be sure to give you best answer.