Can an 18 year old female get stomach cancer?

For the past 6 months I have been throwing up my food. I had thought it was stress so I didn't worry too much about it. It has started to get worse. My doctor had a barium swallow done and that showed that there was a lot of baium still in my stomach at the end of the procedure and nothing was wrong with my intestines, Then he had a gastric empying test done and that showed that my stomach isn't empying out the way it should. When I looked up gastroparesis on the internet it said that it could be caused by a bunch of things but the only one that would really fit is a ulcer or tumor blocking the exit. I have an Upper endoscopy next week but I've been freaking out since an ulcer would have been hurting really bad. I was just wondering if anyone knew anything about this?