Im not sure I have any real advice either here.. but..
I went through this with my husband after our daughter was born. Having sex maybe every other month, bickering a lot in between.
In my experience only.. that bickering for me was a sign of sexual frustration.
Little things that really are no big deal.. ( mis placing plates in the dishwasher, clothes hanging out of the hamper.. etc) were just ways to vent my unhappy feelings.
It was only AFTER we started having sex more often that those behaviors went away for me .
One thing I learned is that my issue was , I was waiting for my BODY to say ' lets have sex'. If I wait for my personal cycle, that amounts to only two or three times a month if Im not tired, stressed, working, busy, cleaning, sick..( you get the idea)
Other then that I am on neutral.. and that is normal.
For women, we usually have to start having sex before we feel like we are WANTING sex. Not the other way around. Men feel 'horny' then want sex..
We have sex, then feel 'horny' We are strangely wired that way..
Once I learned that though, having sex was no big deal.
For a while I really thought one of two things-
1) Maybe i was not truly in love with my husband
2) having a baby destroyed my ability to want sex and I was sort of doomed.
Thank goodness neither are true. It was simply a situation where I just needed to start doing something different and stop thinking that I had to be so excited about sex before I could have sex.
Add on to that time between me and my husband -my pregnancy- where we could not really have much sex. When I finally realized what was going on, counting the nine months, we were going on almost 2 years of this no sex pattern.
I have had many pregnancies, but only 2 babies. My body does not do well with pregnancy and we were scared to bits about losing our daughter. So sex was just not an option during pregnancy, but that attitude continued even after she was born.
Even though I had a real, concrete reason to not have sex during pregnancy, your wife might be feeling some kind of body change now too where she thinks she shouldn't, cant, or doesn't enjoy sex anymore and it may feel concrete for her as well.
Being out of practice does that
I wish I could say that all it took was A , B , or C and we were fine..
But in all honesty, the problem was with me and me alone. Not him. Not 'us' ....... just me.
Our daughter is now almost 4 and I am just now comfortable with admitting what happened.
If that helps you understand how slow the process is...
I don't really have 'advice' and for that I apologize.. but I did have an experience that sounds almost exactly what is going on between you two ( from what I read) ... And I just wanted to throw in my 2 cents in hopes it helps some where..