It seems we always hear about Guys thinking with the wrong head all the time. What we don't hear about is that a lot of Women seem to think about sex about as much as we guys do. LOL
It's ok so long as it doesn't interfere or cause problems in other areas of your life. I can't count the number of difficult shifts I have gotten through at work by taking a moment to think about the beautiful woman waiting for me to get home and how we might say hello to each other when I got there. That being said though, after just a moment of that luxury, I had to get my head back in the game and do my work.
As you are with someone for a while, you learn that each of your sex drives will fluctuate over time and not always in sync. with each other. Routine and predictability is good to a point. It helps us be comfortable with each other. BUT! A spirit of adventure and willingness to explore helps keep an excitement in the relationship. THE DIFFICULT part is striking the right balance of the two.
Don't forget to keep a healthy sense of humor! It will get you through a lot of situations in life (sexual and otherwise) which are boring or difficult or embarrassing.
BTW, I'm glad that wife thinks about sex as much as she does. Her ideas have taken us some interesting and slightly kinky places I never would have thought of much less asked her to participate in. Nothing severe mind you. We aren't into swinging or stuff like that, but some of the positions she has come up with and role plays she has suggested have been REALLY HOT!!!
good luck, you're apparently as normal as any of us.