Vocation motivation

While I know that I really should be motivated to work for the sake of being productive and doing something worthwhile, the fact of the matter is that given the choice, I wouldn't work. The thought of doing whatever the heck I liked all day is really quite appealing. The thing is though, that I work so that I can provide for my wife and child, and make a life for us that keeps us happy, healthy and safe. Money is a big contributor to those three goals, so I work, and that keeps things good.
But recently, it's been a bit different. My wife is a stay at home mum by choice, but recently our son has become quite a handful. So she spends her days getting progressivly more tired and stressed, until I come home of an evening, which is a time she builds up in her mind as being her point of relief and respite. However, I come home tired myself, and would love nothing more then to sit down and have a rest. This makes her not happy. Meanwhile, valuable time I could be spending with my little boy ticks away while I try and recouperate from the days' work. Not that my job is particularly harsh - it's just a full day of work each day. My wife isn't interested in doing anything, because she's cactused from the day with our son, and so we all are generally unhappy until we go to bed. We then get up, and do it all again.
Why am I doing this? We were a heck of a lot happier when we were living off Centrelink while I was at uni. We spent most of our day together each day, and so I could help my wife through the tough spots. True, we didn't have our son then, but imagine if money was no object for a second. We could divide the stress of caring for an almost 2 year old between us, and get to the end of the day happy and not overly emotionally drawn. He'd be better off, we'd be better off, we'd just have a lot less money. Instead, I come home each day to a woman who would be happy to see me if she could muster the energy, and who is disapointed because she can immediatley tell that I'm not overly keen to spend the entire evening minding our son while she sleeps. I was alright when I was working a job with short hours, but now that I'm working a normal day, I just don't have the facility to come home and be our son's only source of entertainment. Couple that with the stress from a new job and trying to buy a house, and I'm just about ready to check myself in for a few weeks at the sanitarium.

Anyway, that'll do. I'm just having a smallish vocation crisis. I'll be OK shortly I'm sure.