This post has been running through my head all night, so what follows is a jumble of all the things I want to say :)
1. This doesn't seem to be a finance issue to me. This is an anxiety issue. (nope, this is not a 'diagnosis over the internet' - I don't mean Anxiety(TM) - just using the word in the average every day sense. But, if it does feel like it is taking over your life, you might want to get that checked out all the same).
- you've already stated that your wife's spending is pretty much fine.
- you are aware that it is your issue, and not hers
- it sounds like there really is nothing that your wife can do to make you stress less about this. Her spending is NOT the problem, and this is not a time in her life when she can make managing your emotions a high priority - she has enough of her own crap to deal with right now.
- your emotions are yours to deal with. If you need to offload them on someone, then please DO so - just not your wife right now. A journal, an anxiety workbook, a therapist of some description might all be well worth considering if this has become a large enough issue that you are turning to internet strangers for help with it.
2. The post-partum period lasts for aaaaages. I am currently expecting baby #4 and I know of what I speak. There is this weird idea out there that women can pop out a baby, head home that afternoon, breastfeed like a ninja and be in the swing of the 'new normal' in the space of a week or two (at most). It is a complete and utter lie. Sure, there are outliers that that may be true for, but it is by no means a normal experience. Your wife is (likely) currently experiencing a clusterfuck of hormones, expectations, exhaustion, crying (both her and the baby), wondering what the hell just happened?, who is she anymore?, I wanted this baby so badly but I'm not having fun yet, this sucks and am I the worst mother in the world for even thinking that? Oh G_d the baby is hungry again and I don't know what I'm doing!!
This stage can, and often does, last for several months. Some of us call it the '4th trimester', to help us remember that this is not normal yet. The newborn phase is still all part of the pregnancy/birth thing and nothing approaching the new normal will happen until about 3 to 4 months in.
Do not be coming home from your long commute, long work day and yoga session to spray your own anxiety about money into this mix. It will not be pretty.
Also, don't underestimate the skewing influence of fatigue on your own thought processes.
[edited to add: just saw this article and thought it relevant:
http://www.huffingtonpost.com/sarah-bregel/what-postpartum-moms-really-need_b_5343907.html]
3. Saving money is awesome. Because money makes life easier. The early retirement thing is about making life *much* easier, sooner than most people get there. But there is more than one way to do it. Maybe you need to step away from the Money Mustache ideal for a while. He did the double-income-no-kids thing at a high enough income and for long enough to hit FI before starting a family. Most of us have not done that, and you are now in that second category :) The phase of the double-income-no-kids savings sprint is behind you now - even if you keep a double income, the kid related expenses are high, not least of which is childcare. You are now in the 'slow and steady' lane. And you have a fantastic head-start compared to others your age.
4. These different stages in life come with different money priorities. Heating a house so that the people who are actually in it all day are comfortably warm becomes a priority when one of those people is a newborn. Food that is easy to prepare, including *gasp* takeaways on occasion is a lifesaver on those days when everything has turned to shit (sometimes literally), the mom is still in her pyjamas at 4pm, and she's hanging by a thread. That is what money is for. It is for spending - either now or later - but life with a newborn is one of those times when 'now' can make a lot of sense. Remember, this is not the new normal and things will settle down in a few months, as everyone starts to get more sleep. You're in this for the long haul, and 6 relatively spendy months is not going to make a big difference overall to your retirement goals (given your overall frugal pattern) but it could make a big difference to the sanity and happiness of your family unit.
5. Expect your utilities to go up. This took my husband and I by surprise back when I stopped paid work, but it makes sense. Instead of the house being empty and basically shut down for 8 to 10 hours a day, it is being heated, and coffee is being made, and lunch is being cooked, the computer is on, water is being used, the fridge is being opened... This is NORMAL. This will happen. Expect it and do not start looking for the culprit - the culprit is the joint decision your family made about what would happen when you made a new person together.
6. The ceiling ventilation. If you don't know what trade will do it, phone a big-box hardware store and ask them for a recommendation. Say "I'm thinking of doing this myself - is it a DIY job, or does it need a pro? And if so, what sort of pro?" If they say 'it's a DIY job if you have some experience', then have a look in the yellow pages for a 'handyman' or 'property maintenance services'. If it needs a pro, then contact one and ask. The answer may differ depending on your local regulations.
For example, where we are, we can instal the ventilation tubing ourselves, and the outlet vent etc, but any wiring *must* be done by a certified electrician. Depending on what you need to cut through to put the exterior vent in place, you may need a real builder instead of a handyman, but the process of getting the 3 - 5 quotes you'll be getting (right?) you'll be able to work out what you actually need done.
Good luck. This too shall pass :)