Hi Melissa,
If your peep is sick, and you treat him/her with the medicine for their illness, and then not too long afterward is showing more symptoms of sickness THEN you need the doctor consultation. When that happens there's usually an underlying infection...sometimes a fatal illness that if not taken care of may kill your little peep.
I just took your advice for one of my little guys who keeps getting headaches and sore throats. The doctor suggested the vancomycin and an anti-inflammatory, so I followed the directions and got the award for curing a grave illness.I was shocked, I didn't even realize he was that sick!