Hi N.,
My daughter had similar problems. Whenever she got a cold/runny nose it would always turn into this horrible cough (especially bad at night). We finally took her to a pediatric pulmonologist who diagnosed her with infantile asthma. (Pediatrician office would always down play when I brought her in...she was sick at least 1-2 times a month!) For her the trigger was colds but allergies could also be a trigger. She did not have the tipical wheezing that you see with regular asthma.
They started her on nebulizer treatments then to taking singular (chew tablet once a day). This started around 5 months and now at 2 she rarely has coughing episodes.
Here are some of the things we did to manager her cough:
lots of fluids to keep secretions thin and easier to cough up.
for night time (coughing was keeping her awake and she would get exhausted):
*humidifier
*vapor plug in
*cough suppressant/expectorant (make sure package indicates ONLY these 2 conditions so that you are not giving uneccessary medicines). We did this only at night and only when coughing was keeping her from sleep.
*Other alternative to cough medicine is honey (but she is not old enough for that).
I would recommend checking with your pediatrician about cough medicine for guidance. Also askdrsears.com is a great resource. Dr. Sears has posted charts for symptoms and suggests when and what medicines are appropriate with the correct dosages for 2yrs and under.
I know that making a decision to give your child medicine is a tough one with all the unknowns out there.
It was terrible for us seeing our daughter always sick and coughing and coughing and how exhausted she got. She also did not gain weight during that time due to being sick and we had to start working with a nutritionist.
In our situation medical treatment was the best choice and its benefits outweighted the risks of the medicine. I think this is something to evaluate in each individual case. You might give the zyrtec a try and see how it goes-and you can always stop (if this is allergy related she may only need to take it during the peak pollen months).
Good luck!