Suggest Treatment For Flu Symptoms Like Headache, Nausea, Lethargy, Appetite Loss, Abdominal Pain And Vomiting

My husband is having flu like symptoms. He had a flu shot one week ago. Currently Temp 100.2 headache, nausea, lethargy. He had a work up to rule out gallbladder issues on 10-7-18 after severe abdominal pain and vomiting. No appetite. He is having EGD tomorrow and doesn t want to take anything for pain until after the EGD. Any ideas about what his problem could be. Age 67, white male, active. No health issues.