Brian:
I understand what you mean when you exert all of your (limited) energy on putting up a brave face for the people at work, and then having nothing left for the most important people in your life at the end of the day. I put on a brave face for four years in my last job. As time went on, each day got to be more harder than the last. I would wake up with a headache and limbs that felt like they weighed 800lbs. each. It was all I could do to get out of bed. I started coming in late, and often left early. Sometimes a needed a break at lunch too. My company kept me on because I was a well respected by my clients and colleagues and I always managed to stay on top of my work. One day I went home for lunch, and could not go back. I stood at my front door staring out the window and crying. I couldn't leave my house and it was physically painful. I eventually told my manager and he was surprisingly understanding - his wife suffers from MDD and cannot work at all, so he could really relate. They offered me some flexibility in hours and kept promising to find someone else to help me with my workload. Against the recommendation of my psychiatrist I left my job and decided to go back to school so that I could work for myself. I loved school and was able to spend more time caring for my family. Unfortunately, money became an issue and I had to start working earlier than planned. I do really enjoy my new job (most of the time) and have been able to manage my workload so that I can stay in bed all day some days if I need to. The point of all this babbling is that for me, a change was what I needed. I don't think it would have mattered what I changed to, but I felt than when I was at my old job my anticipation of feeling down and exhausted made me feel more down and exhausted. There are still a lot of challenges now that I am working for myself - in fact in some ways there are more. I am hoping that the CBT will help me break these negative cycles of feelings so that I won't need to make such a drastic change in the future.
I also agree with Patrick that it would be good to sit down and discuss things with your wife. At one of my lowest points I was constantly consumed with the idea that my husband would leave me for somebody 'better'. He would get very frustrated with my insecurity because he felt that he was showing his commitment to me everday that he supported me. I finally had to say to my husband that I knew that I was difficult to live with although I could not understand exactly what he was going through. I made him promise me that he would be honest with me if things were getting too difficult so that I wouldn't be constantly worrying that there was something he wasn't telling me. Sometimes he gets frustrated with my lethargy (I can't blame him for that), but he always tempers his frustration because he knows that I am not being this way on purpose.
As for the medication. I had the same thing happen to me. I think the initial burst of positive energy is somewhat of a placebo effect so try not to get discouraged. It takes a long time to figure out the right combination of drugs, but it will be worth it.
Hang in there. I think that this is a good place to be able to express your feelings, and I find it comforting to know that there are others out there that can relate to where I'm coming from.