Nighttime coughing can also be dustmite allergy. Just throwing that one out there.

One way to check is to:

a) put inexpensive encasements on mattress and pillows,
b) wash bedding in HOT water (and dry on the highest heat setting permissible),
c) stuffed/soft toys-- wash in a pillowcase, then stick them in a freezer for a few days, and this will both remove dustmite poo (the allergen) and kill the critters themselves.

If that helps significantly... then dustmite allergy is pretty likely. We wash bedding pretty frequently (at least weekly is advised for dustmite allergy).

Schrödinger's cat walks into a bar. And doesn't.