Dona is absolutely on target! What follows is a very long post but maybe it can help you to "walk a mile in the other person's shoes".
Perhaps you should try a little exercise for the imagination. Take a moment, close your eyes and try to envision your wife. Take a few deep breaths, and imagine that you are her, and that the following scenario includes the secret thoughts that you (as your wife) are having.
My day started at 5 am today. I was roused from sleep by the cries of my baby. I love her so much, but I'm really getting sick of the hours of this new job as "Mommy". We sat down to breastfeed and it was so nice: quiet, solitude, and just reveling in the emotions of sustaining this new life that I adore so deeply. I do my best to enjoy this moment, because I know it's probably the last time I'll feel truly relaxed today. I send my husband off to work this morning with a hurried kiss and a little pang of regret that I was too exhausted to do anything but crash into bed after the late feeding. He must be getting lonely for time with me too. For the rest of the day I alternate between changing diapers, doing laundry that smells like sour baby puke, soothing my crying angel to sleep, and trying to decide what to fix for dinner. I go shopping, pay the bills, do the dishes and collapse on the couch for an hour when the baby naps at 2:00. The most stimulating dialog I have is with the checker at the grocery store, so there is a lot of time to think. Some of the things I thought about today were: " Baby seems kind of hot, I wonder if she's teething. I should really eat better, I'll never get my body back at this rate. My breasts are killing me, is that kid ever gonna wake up and relieve this pressure? I bet hubby was pretty disappointed last night... I know it's been a while. Why am I so tired, it seemed like a slept pretty well last night? I guess it's just the extra calories I'm losing with the breastfeeding. That coupled with feeling dehydrated and the hormonal swings just really takes is out of you. Am I going to be a good mom? What if I make a mistake... a big one? Hey, she bit me that little stinker... now that nipple's gonna hurt all day! "
Now hubby is home and what a relief! I hand him the baby that's been crying half the afternoon and go to the kitchen to make dinner. We eat in shifts since baby won't settle down unless she's being held... yep, probably teething. But what if it's an ear infection, how do they expect parents to know the difference? We don't get to talk much, but it's good to have him home. He's so good with the baby... what a great dad... God, how I love him. I breastfeed one last time (I hope) and baby finally goes to sleep. Maybe we crash on the couch and watch some mindless TV to relax. Hubby gave me a neck rub and I almost fell asleep... nice.
We get into bed now and boy does it feel good to stretch out. My shoulders are killing me from carrying baby and breastfeeding in a dozen different positions trying to get comfortable (note to self: try not to slouch so much). Hubby snuggles in and I'm about to drift off when he kisses my neck. I stiffen. He's interested and I'm exhausted. Oh well, the poor guy deserves to have some fun... he's been pretty tolerant of all the changes lately. I hope this goes better than last time. I'm worried that it's going to hurt again. So we're kissing, and I wonder why I don't feel excited like I used to. Hormones I guess, let's keep trying. He's caressing me now and it feels nice but I'm having trouble concentrating... I'm worried because it's taking so long to get the engines revved. Every time he touches my breasts I tense up a little. I know on an intellectual level that this should feel good, but these things have a higher purpose now. Bizzare notions that using them for sex is cheating on the baby and vice versa cross my mind. I try to push these thoughts away, only to wonder if his attention to my breasts might cause 'let-down'. I'd be absolutely mortified if I started leaking milk right now! Uh-oh, his hands are headed south and I'm not even wet yet. I'm failing! What's wrong with me, this always worked before?! I tell myself to stop it, just concentrate on the physical and quit thinking too much. It looks like we'll have to resort to using lubricant again. I feel like a failure. I'm broken somehow... my body just doesn't respond like it used to. Can he possibly understand? Does he even want a woman like me any more? Oh please don't let it hurt this time!
Ok - now tell me, do you feel sexy right now?
Please be patient with her. I'm not saying I can read your wife's mind, but there's more than just hormones at work here, and the hormones are pretty significant. She's probably just as concerned about the future as you are.