Life is hard... It's hard to feel like you're making a difference and that you're worth it...
But you are. You're doing something you don't want to do to support your wife and baby. That's HUGE. They are SO lucky to have you!
Keep it up. Things WILL get better, I assure you.
On a chemical level, consider getting your testosterone checked. I've had depression for many years, and only recently discovered that my testosterone was low. I've been treating it since, and it's made WAY more of a difference than the antidepressants. Contact a Hormone specialist, seriously.