Amy Schumer’s 3-year-old was hospitalized with respiratory syncytial virus last week while she prepared to host “Saturday Night Live,” the comedian said Sunday. The Manhattan-born comic said she missed Thursday’s rehearsal for the NBC sketch comedy show when son Gene was admitted to an emergency room amid a surge in cases of the virus that largely affects young children. “I got to be with him the whole day at the hospital and the beautiful humans at [’Saturday Night Live’] couldn’t have been more supportive,” Schumer, 41, wrote in an Instagram post. “My son is home and better. The reason this …