ER Dr. says its erosion of throat, stomach poss. intestines

My 26yr. old son had to go to emergency the other night because felt ill; he had nausea, abdominal pain, bloatness, diarrhea (these symptoms 4wks).  He doesn't eat well, drinks hard liquor and every day has 3-4 xtra lg cans of Monster energy drink.  The ER. Dr. told him that he acute  erosion of the throat, stomach/intestines. Dr. only asked questions of his habits, and labs done,but I'm not aware of how the labs  came back, my son said they were okay???? Dr.gave him pepcid & donnatel for pain; and was told to follow up with his GP.  The literature he was given was for gastritis, diarrhea symptoms;  the problem is my son doesn't want to go to the Dr. due to testing they might have to do; he does not have a primary doctor.  His x-girlfriend told me last year that he has  had stomach problems (diarhea (diarrhea), smelly stools) for a year now. I'm so worried that he could have something really bad; I need to convince him to go. What could happen if untreated, how long can he take pepcid & donnatel for?  Concerned Mom. (he's drinking since his breakup with girlfriend :(