Plain and simple, a short manual on wife-keeping:

She's cooling off because you haven't been servicing her properly.

She doesn't have a headache, you just have to romance her better. Get busy. Start slow, keep going and be sweetly persistant. She's saying "no" because she's not interested in a quick hump.

Her pleasure is your goal, not your own. Stop rushing the end game. Practice the art of massage. And patience. Practice makes perfect.

And know this, all you bozos who haven't realized this yet:

Making love is NOT something you do when you want sex, it's a huge collection of little things you do all throughout the week, like a short phone call just to say "hi, I'm thinking of you", and it's a quick hug before you leave and as soon as you get home. It's saying "thank you" when you notice the place has been cleaned or food is being served to you. It's commenting on how pretty she looks.

Every freaking day you keep the fires burning with some kind comment or you let the fire go out because you don't care for her happiness.

If you can get her chemistry ignited, everything else is fine. Take care of her, and she will take care of you. Or at least you won't care that the house isn't spotless.

Get busy.
NOW!