im sorry to hear you are so unwell!
i have functional dyspepsia a chronic stomach disorder so i know how fustrating it can be!!
But i seriously doubt u have cancer, as stomach cancer is sooo rare at your age! i even went through thinking i had it too!
Have you thought of gastritis?? that sounds very likely considering what u r describing! its inflamation of the stomach lining and causes all the symtoms u describe even vomiting blood! as the lining is soo damaged.
Hpylori is a bug which causes things like gastritis and ulcers, gastritis can take a long time to clear but it is curable (unlike my condtion)
Antibiotics tend to be less effective in time so i would seriously consider taking a herb called mastic gum for a few months! it has been found excellant in ridding the body of hpylori! and will be a very good move for you
aloe vear juice may help calm the pain too and mabie stop the vomiting if the pain is calmed down!
Let me know how you get on and if you need any help with where to get mastic and other suppplements, or just advice! i have become a wizz with stomach disorders!!