D.B.
I think you're seeing sexism in action. We women are so conditioned by society to be the "fixers" that, if something goes wrong, it's either our fault, or at least our job to remedy the situation. Instead, try looking at some of this as you being a grown up and a bit impatient with other people's nonsense or lack of responsibility. Maybe you're not losing your mind, but losing your patience.
If there's a drama mama at school, that's her. It's not something you caused, most likely. All you can control is how you react to her.
If your husband is being a butt head, why isn't that on him? Maybe he's just being a butt head. Maybe he's depressed or stressed. But blaming you for everything? Maybe he thinks you're an easy target because that's so much easier than accepting responsibility for his own problems or for venting in a healthy way. So, walk away from it. Stand taller, don't shrink away.
So the trainer is MIA - that's frustrating if you found someone you like, but just because the trainer has problems in his/her life or because the pay is so low that he/she went elsewhere (or whatever it is) doesn't mean it's your problem. Maybe some of the class members are reacting to that. Maybe they've been in the class too long and need a different kind of routine - I'm about to move on from my own long-time class as well, because the instructor is just going through the motions and not really teaching or paying attention to help with form or technique. Maybe some of your classmates are injured or stressed and need a different type of strength training or something like yoga. Maybe they have a medical problem and have instructions to change something up. Maybe their husbands are being butt heads and they are switching their schedules to accommodate the men. But the main thing is, why assume you are the cause of this?
Being a hermit was, apparently, unsatisfying - so you changed it up. Maybe you had kids and decided you had to be out in the world. Being alone is a great thing in many ways, but avoiding getting the mail because you don't want to speak to anyone after a week is a little more than I'd be comfortable with. If this is a sign of depression, think about getting some help. Maybe you're reacting to the end of summer and the shorter days/cooler temps and not doing well with that. Seasonal affective disorder and similar conditions affect people's moods.
And you go back to that societal pressure at the end of your post, saying you have to get out of the slump "for the children's sake." What about YOU? When do you matter? When do you get to come first? Maybe you have a kind of malaise because you're always putting others first, and you're having a hard time finding anyone to put you first. It's a good idea to give everyone something to do rather than let it all fall in your to-do pile. Give every kid a chore, and take an entire day off sometime on the weekend and let your husband cope with everything - kids' schedules, getting them dressed and fed, finding the stray sneaker, and oh yeah cleaning a toilet and preparing dinner. Maybe you'll feel appreciated. Meantime, take the day and go do something FOR YOU that no one else likes doing, and don't make it an errand for them. Go to a museum or have lunch with a friend or walk in the woods - or all of those things, and don't apologize to anyone for needing to nourish your own body and spirit.