Hi , in my opinion you have severe throat infection
Penicillin is the drug of choice but when oral tablets are not working which means infection is more.
So you need intravenous antibiotics.
If I were your treating doctor I would have asked for a throat swab for culture and sensitivity.
Routine blood counts to see the level of infection.
Depending on the reports I would havd decided the antibiotics to be given.
Along with this anti inflammatory drugs, beta dine gargle is also advised.