You are anxious, probably, and that's why you are getting sick. I have had such severe bouts of anxiety that, when I've gotten my blood tested (for imagined illnesses of course), my while blood cell count will be extremely low. If you are anxious then your body puts all its resources into now, and not the long term (ie the immune system). Also you have a baby- you are probably sleep deprived. My husband and I have both been sick more often than not since we had our daughter (I posted on this same thing a few weeks ago). I've had a gazillion colds, the flu, bronchitis, a sinus infection, the stomach flu, you name it! The sleep deprivation couple with anxiety is a very bad combo- they make each other worse.
Anyway, I feel for you, and am in the very same situation (I have a cold now, and had bronchitis 3 weeks ago).