I Have A Boston Terrier That Has Been Sick For Almost A Year?

my dog started vomoting ,passing blood and losing weight last summer, he was in the hospital for 5 days and 3 parvo test came up neg, the vet never found a cause for his illness. since then whenever he gets hot the symptoms come back and also he keeps losing weight even though he has a great appitite. has anyone else ever had this problem with their dog, he is also negative for worms