I just got immune system treatment Gamunex on Thrusday, now I'm feeling flu like symptoms like sore throat, nausea, and fever. Do I go to the hospital?

Yes please. for whatever indication you received the Gamunex for, please follow up with the treating physician/ team, that could just be a viral infection, or may be you need a booster, again I don't know which route was used (IV or SC), good luck.