your not the Energiser Bunny
I was getting to that. Neither is she.
If you don't fancy several weeks on the sofa I suggest a compromise. Treat her like the Godess she is. You'll be suprised how quickly she will be able to revive her lustiness for you when she is showered in non-sexual attention.
It's hard for a woman to go from a household drudge to a sex siren. It gets more difficult as familiarity with ones partner (and his unfailing ability to make a mess) increases. If you want to hold onto the lust you have to bullshit your way through. Be the Love Slave, not the lust broker. Oh, and clean up after yourself. That goes a long way to making her feel special.