Long lasting respiratory infection....

My daughter has had a respiratory infection for two months.... you heard me right two months. She's been seen by three or four different doctors (3 in separate offices) who have all diagnosed her with respiratory infections. They won't give her anything though. We went back in today because she had pink eye and they said she still has this damn infection.... I'm at a loss. how do we get rid of it? she's 22 months. can't take any decongestants, she has a humidifier and lives in humid fl, we let her sit in a steam filled room, she rests, she drinks plenty of fluids, and we even started essential oils which haven't helped. any advice? please.