Flu signs for 4 weeks. mono-negative. finished zinnat. doc gave voltaren, (diclofenac) amoxycillin and flagyl. red, sore throat recurs after medication ends. why?

Abscess?: For the purpose of this interaction, I'm assuming, by "flu symptoms" you mean fever, chills, fatigue etc. In my experience, recurring sore throat and "flu symptoms" could indicate an abscess which are kept under control, but not completely eradicated, by antibiotics. See your doctor again and, if necessary, get a referral to an Ear, Nose & Throat doctor.