of it is perhaps not paying enough attention to your emotional health. Talk to your wife about it if you can and see what thoughts she might have. Sounds like she's fairly occupied in her education though, so be sensitive to that.
My instinct in these situations is to just suck it up and keep your head down while you do your best. Sort of fake it till you make it. I'm not sure that's the healthiest path, but it's the one I've traveled many a mile on. It turns out there is something good about just going through the motions; make sure you're doing family prayer and scripture reading every single day (seriously, never miss family prayers morning and night - never miss, especially while your kids are young enough that you control their schedule), go to church, have family night (another thing to never miss), and family outings.
I don't know what to tell you about your hobbies - outside of BYU football I'm pretty sure most of the hobby type things I enjoy in life haven't been a part of my life for a long time. Heck, I'm not even sure what my hobbies are anymore; in fact, I may not really have any! I am in the stage of life where I should be able to fire them back up, and I think I'm slowly coming around.
You're just in the stage of life where you need to keep your head down and keep on keepin' on. I understand that's not helpful advice for people with depression, but I don't have any other advice because that's how I did it.