What are the symptoms, treatments, and effects of whooping cough on infants(premeture) and adults?

Me and my wife were told that our three month old daughter( she was born 1 month premature) might have whooping cough. I say might because one doctor said yes another said he wasn't sure and another said she had it but it was okay, and none of them precribed any treatment. We have already seen three doctors over this and still no results, we don't know where else to turn.
Our daughter's symptoms are: coughing until she vomits, she can't sleep, she won't eat, when she does sleep or eats she coughs until she wakes up or vomits what she just ate, and she has a lot of snot, coughing it up and runny nose. we have given her decongestant cough medicine but nothing helps.
If anyone can give us answers or even some helpful advice, maybe what to do next, we would be very grateful.

As a Pediatrician, I have seen a few children with Pertussis or "whooping cough". Infants usually have the symptoms as you describe-- they seem peaceful one moment but then go into paroxysms of "whoop-like" coughing and vomit ting. These whoops can also be associated with fetal hypoxia (low oxygen levels ) .These "whoops" are usually preceded by about 2 weeks of a "regular" cold , with congestion and slight coughing.
Also since most adults are not immune (there is a new tetanus Vaccine that came out about 6 months ago that protects adults against Pertussis, but very few adults have actually received it),
someone in the family will usually have a "chronic" cough since pertussis is very contagious.
Also since Pertussis cultures/titers take a long time to come back-- it can take weeks until a definite diagnosis is made, but the Department of Health still needs to be notified, and can hasten lab results(Pertussis is a reportable disease).
Also in your situation, your infant with these symptoms at 3 months of age should probably remain in a hospital and be closely monitored and given oxygen as needed with appropriate blood work and x-rays. (may want to contact a tertiary care center if one is available nearby).
If your child doesn't have Pertussis it could still be RSV (which can be diagnosed sooner) or pneumonia.

Good-luck

I don't know why you have no results. The doctors can do a throat swab and request bordatella pertussis PCR, I should hope.

The medication shown to be effective for bordatella is erythromycin.

Get her seen by a real doctor

Her coughing should sound like barking, which is the tell tale sign. With such a harsh cough it can cause some upper airway swelling which you can usually tell is happening when the baby starts to drool more than usual. You should be treating it with a cool mist humidifier, breathing treatments, and possibly antibiotics. If you have a bulb suction definitely use it. You should probably have a RSV wash done also to rule that out.