My Son Is 2weeks Post Tonsillectomy And Vomited A Lot

My son is 2weeks post tonsillectomy and vomited a lot of blood, which doctor says he had been bleeding slowly for days, but he has had a fever for three days now. Can the blood in his stomach for so many days cause a fever? And if so is it normal to at least three days? He has no other symptoms except being pale. He is acting normal.