Why he throw up almost every day?

He,my boyfriend, throws up almost every day and this has been happening for a while. It really scares me. He's been to the doctor at least a dozen times. At first, they said he was throwing up from drainage cause he had what they thought was a severe sinus infection, but after taking medicine for 3 weeks they sent him to a ENT doc to find out it wasn't a sinus infection at all and his sinuses hadn't even fully developed on that side. They then proceeded to put him on acid reflux medicine he said it didn't help and he was still throwing up, but I'm not positive he was actually taking it. He is also tired ALL the time and has trouble sleeping. I think it might be caused from stress, because he has really bad anxiety but he won't tell the doctor cause he thinks all they will do is send him to a psychologist and he doesn't wanna do that. He's only 16 and he is on so much medication it scares me. They have him on ambien now and he still doesn't sleep. I don't know I think he is too young to be on all that medicine and his doctor can't figure out what is wrong but he refuses to see any other doctor and screams at me anytime I mention him going to another doctor. He misses almost every day of school cause he is so sick, but he gets a doctor excuse for all of them. Either way it scares me. Please help :(