I think it's called tired, well more than tired, exhausted!!!!
When you are pregnant with the first you have so much more time to yourself, if you need a sleep you have one, if you need to get out of the house you go etc there are no worries about little ones sleeping through or being interruptted during. I think it declines more as you have less time, sometimes I don't even have time for myself let alone someone else!!!! Good when you have an understanding DH, and great you are prepared to reward him for his patience. Quality over quantity, I say.