Heavy Mucus in a 17 month old infant

It appears that the infant always has a runny nose. The mucus is very think, sometimes cloudy, but very seldom clear. It seems to just come out of nowhere, it does not appear she has a cold, but she is always full of the mucus. There are times when she carries a fever constantly, others not; but she stills is always full of mucus.
After numerous visits to the doctor, the anti-botic medicine is always the same and never clears the problem. Is there a specialist available for this type of problem, so that tests can be ran to better understand what's really going on.