GP's probably right that it's a virus, why do you think that antibiotics will make a difference? Choice of antibiotic difficult if baby is truly allergic to penicillin and erythromycin. probably would need a throat swab to get it right.
If you're not getting any joy from your GP and you think she's getting worse rather than better, take her to your local A&E department. If you have a children's hospital locally with an A&E, even better.
my dd was very sick with tonsilitis 2 weeks ago, and I was giving her ice poles and icecream. Also calpol and kids ibuprofen but I think your dd might be too young. Can you see if there are any white spots on her tonsils. It will give idea of whether bacterial or viral. (ie white spots more likely to need antibiotics.) My dd illness went on for 10days so think there is a nasty bug in the air. HTH