You’ve got plenty of stressors - and sometimes stress can manifest itself in apathy and boredom because you just don’t have the energy to appreciate the good things in life. It sounds like you have it in perspectives (could be a whole lot worse ...), so this phase may jut be something you have to ride through until your energy returns.
I totally get the single-mother-envy thing. I make a good income in a profession that I like and am proud of - but I also work with a lot of people who are either making TWO good incomes, or have no financial dependents, and the next person who complains to me about how they “only” took TWO WEEKS vacation this summer, when I’ve only had four days off in a year, plus this summer dealing with all forms of fallout from suddenly dead ex and trying to help grieving teen ... it’s easy to fall into poor-me thinking - that’s one of my biggest challenges, when I also have a lot of advantages and privileges.
For me, exercise does wonders. I know everybody will be preaching at you to be more active, especially if you’re trying to lose weight, but it does make such a big difference in my mood if I’ve been able to run or bike consistently. Sometimes it takes a couple of days for the benefit to show up, but it’s there.
Also, go see a doctor about your back pain! That’s what doctors are for!