We have some similar issues. (coughing, and also food allergies). One thing that has worked wonders for us is Hyland's brand C-Plus Cold tablets. It is natural, not a drug, and it seems to help the congestion/coughing right away. (ours seems to be caused by post-nasal drip mainly). They dissolve easily in the mouth even when sleeping!
We've also used mangosteen juice w/ some success for the asthma symptoms and now rarely have to use the inhaler.(but this is a much pricer venture).
Also, you may notice a lot of aerial spraying (big X's in the sky)of something going on (weather modification?) that seems to cause these kind of symptoms in people. That may or may not be the problem, but it's one possible cause.
We too had major food allergy problems and weekly throwing up for a while. But, for whatever reason, now we're not having that problem now they're a little older. For us, that seemed to be food-allergy related, but not sure.
Anyway, hope some of this info helps you somehow. Best of luck to you, and hope you figure out the problem.