Coughs usually are worse at night...especially with asthma. Do you have reflux? Because a bad cough at night could also be that. I know when I'm sick, my reflux gets worse and my mess don't really work so my cough gets worse as well.
Honestly, as an asthmatic, my pulmonologist does not prescribe me cough medicine. He WANTS me to cough as much as possible. Anytime I've been on a cough medicine I've ended up with bronchitis or pneumonia.
One of the best things is usually just either a very warm/hot shower or just sitting in the bathroom with hot water running in the bathtub to get the steam and heat from it....usually helps me at least a little bit with the congestion and cough. However, I will admit it doesn't seem to be working for me this time around.
I'm on antibiotics, prednisone, pulmicort (inhaled budesonide), xoponex, Zyrtec, singular, Prilosec, Zantac, and Benadryl and I still can't get rid of my cough. I've given up trying at this point.
I am sleeping either with 3-4 pillows or on the recliner right now so my head is elevated. That seems to be helping the best. If you haven't elevated your head at night OP, I would definitely try that.
Good luck OP. I completely understand how your feeling with this dang cough!