Maybe this has been discussed before, sorry i didnt read all 160 pages in this thread. So forgive me if it was already discussed.

But you say you have 3 kids and one who is 18 months. Did you notice any changes in your wifes mood after she had her babies? Did it get progressively worse after each one? Is she a SAHM or does she work? What I am getting at is that could your wife prossibly have post partum depression? That can totally impact her self image, sex drive, and a host of other things. I personally know this as I had severe PPD after my first and aftermy second. Its horrible. She may be embarrassed to say that she is overwhelmed with the childcare and you may not see it as it may not be severe espeically if she is good at covering it up and faking being fine.

will she go to her doctor? Her primary care or OB? I would have her hormones, thyroid, and a depression screening done if she is willing.

Just a thought.