Quenton
Most Doctors usually reccommend that you take it easy while you still have symptoms... including not to race if you have a fever, symptoms in the throat and bronchials. Who knows if antibiotics will hinder your efforts, but you can be sure that trying to race or push yourself while you still have symptoms can be counterproductive and possibly dangerous.
You won't be at your best, and you most likely won't be able to reach your best while still showing symptoms. The stress of racing can slow your recovery, and stress your immune system enough to make your symptoms worse, or leave you more prone to a new infection. I've also heard that breathing hard while you have an infection along your breathing pathways can help spread the infection deeper into your system.
Antibiotics don't do much for most respritory infections, because for some reason they're mostly viral. The thinking is is that giving you somethign to take will treat the possibility of a secondary infection due to stagnant fluids, or somethign like that. I've also heard that eatign hot food, and riding just enough to get your nose running stimulates recovery by getting fluids moving, plus it makes you feel better.
I don't know. I hope a doctor has replied to you already. I'd say take it easy while you're sick.