Dog is Puking up Blood!!!!!!!!!!?

My Roommate has a 3 year old Pomeranian Male,(unaltered) he has been puking off and on for the past few months, she has tried everything! the vet has done xrays,blood work multiple times,fecals multiple times and still nothing. the most recent plan is to feed him nothing but Science diet ID wet and dry food and to leash walk him at all times to make sure its not an outside problem while giving him anti vomiting and diarrhea meds its worked for about 3 weeks but he puked last night and today when we got home from work he puked several piles in his room which were nothing but blood. and he has been refusing to eat but does not act lethargic otherwise. the only things i can figure are hairballs since he obsessively licks his hair, and obstruction in his stomach or something to do with him being unaltered or maybe even fleas (hes on comfortis and heartguard) but i still find dead ones from time to time. any vet techs out there with some suggestion?