What can you tell me about bronchitis?

My 13 month old daughter has and I was surprised. I took her to the doctor because she was pulling at her ears(she has alot of ear infections) and she was tired and fussy. The doctor said her ears were perfectly clear but she has bronchitis, he heard alot of fluid in her lungs, but listening to her she sounds normal, no stuffiness, no runny nose, nothing, I was surprised and I don't know alot about this so any info or advice would be appreciated, We did get the humidifier out today.