Help with my guinea pig issue?

My guinea pig began showing symptoms of URI (puffed up coat, not moving) and I immediately took her to the vet. I was given antibiotics to help treat her URI. After 4 days of antibiotics, my guinea pig is still showing the same symptoms as before, and she began to lose fur. I am currently giving her extra Vitamin C, fresh vegetables and fruits. Any ideas as to what her problem may be?