In theory the big airmatresses sound great get you 5" off the ground but in reality the air circulates thus freezing your backside.
You had a closed-cell on top of your airmattress you said though so that should have helped. Next time ditch the 5" one.

It also sounds like your sleeping bag is very much sub-par as 40-45 is not that cold and i'm sure a $30 coleman from wal-mart would work better than what you have.

I think you simply need to retry it with a better sleeping bag and just the closed-cell pad.
The $80 Coleman from wallyworld has served me well as has the $80 MARMOT fromt Sierra Trading post. Both are poly bags rated to -15 I believe.
I've had them down to around 10 with 25+ mp winds and been toasy w/out a blanket ontop of me sleeping in boxers only (no beenie or socks yet).