Winter blues
I'm sorry to hear you're going through a lot all at once. :( It can be hard to determine how much of what we feel is situational, seasonal, normal, abnormal, etc. I think sometimes just talking about it helps and knowing that you're not alone (you're not!!). It's also really stressful not to have control in certain situations (like with work, car troubles, etc), especially when they come out of the blue.
It's great that you're taking a real lunch break, sometimes I find it enormously helpful just to step away from what I'm doing and clear my head. Maybe do something special once a week to look forward to, and it doesn't even have to be going out. Maybe plan to make a special dinner with your husband with music and candles once a week, or have a movie night. You have your yoga class to look forward to, and remind yourself that as obnoxious it is to have to go once a week, I'm going to assume you always feel better when you do. :) I take a class every Tuesday night and while in the winter I hate having to go I'm always glad I go. It helps that I pay for it, so I feel an extra layer of obligation to show up.
But ultimately, you have to cope with stress somehow, and if it helps to camp out in your home for a few days or weeks, and you're not feeling miserable, and you're not smoking... then it can't be all that bad!
And keep in mind... it could be worse. It was -5℉ when I left for work this morning here in Chicagoland, with the high of the day in the balmy, sunny 20s. I'm soooooo glad I'm not having to go out there and smoke 20 times a day.