<human>: My daughter will be 3 in October, and we have already seen her doctor about 3 times for this cough. 

In the beginning of May she had a cold (runny nose, fever, cough) it was gone and came back with a vengeance after about 2 weeks.

She has since recovered from her cold, and now has no symptoms but her cough. 

It's usually a dry (but can sometimes sound wet).

She can cough as little as twice a day as as much as 20 times a day. (Usually in spasms; 2-5 coughs per spasm)

She has gotten an X-ray and it's shown up negative (looking for foreign objects and pneumonia)

The doctor took a swab on Thursday to test for pertussis 

She sleeps with a humidifier in her room every night, but does not cough through the night or when she naps.

It doesn't slow her down and I haven't concluded to any triggers

We have pets, but her door is always closed and we have used an air filter regularly in her room. 

The doctor has only just prescribed an inhaler stimulant to open her lungs when she has trouble breathing but her coughs can be so few and far between sometimes that we haven't used it yet.

Summarize the given text in a few sentences.
<bot>: almost 3 year old has a dry cough for 3 months, clear xray. At a loss at how to help clear this up. Please help!