I can relate, it is hard to balance the loathing/apathy, ambition, and family. Family comes first, so maybe the hours spent on the side project needs to be re-evaluated. If you have a relaxed environment, maybe you can layer your work and side project. Maybe you might find a coworker who also can help out. I would recommend talking to your manager to see what options are available (less hours, more pay, more challenging work). I like to believe good managers exist who would be able to help (somewhere, maybe just not at your place).

I try to make challenges at work by looking at things another way (e.g. switch a programming language or ask for another opinion). That will only increase stress though, so be careful because you might be in a good place if the work is easy and expectations are low.

What is your goal for the side project? Money, experience, or curiosity? Can you find another way to either get more money or more experience that won't involve you spending an extra 5 hours?

I can let you know that in my case I spent a small time looking around and evaulating options ultimately finding a slightly better job. Be optimistic.