Blocked nose (Warning: Maybe TMI)

[Pandora]

Im not sure from what age you can use dimetapp drops, maybe aske the chemist about them as they will celar up the mucuous albeit temporarily.

You could also put a vaporiser in his room at night.

Or get the little fess nasal stuff - I found it difficult to use, but DS was a bit older than your son so he was more prone to wriggling away!