The happiest I ever was as a parent was when my oldest, and then only, was 3.5-4. I worked part-time out of my home as a writer. Ds went to daycare part-time, about five hours a day, and I worked for about three or four of those hours. The other time I spent doing housework, running errands, or taking naps. It was a great center and he loved it. My schedule was completely flexible, so on the days when he said he didn't want to go, which were rare, he just stayed home. On the days when I missed him, I went and picked him up a little early.
But, that was paradise and this is reality. Now I have three kids, I haven't been offered work in almost four months, and I'm struggling with staying at home. The idea of getting up every day and going to a job that I probably wouldn't enjoy, I love writing, and leaving my kids all day isn't an option for me right now. It helps that almost all of my neighbors at SAHM, too, so we can at least hang out and chat over the fence in the afternoon. The mornings are the worst for me. Getting my oldest off to school, figuring out what the two toddlers want for breakfast, trying to get everyone dressed, changing diaper after diaper-- the walls start closing in. My husband has been working crazy hours for the past few months, too. Usually he is able to take off whenver I have an appt. or if I'm just having a bad week but he hasn't been able to do that since about January. That makes such a huge difference. We've still got another month to go.
It sounds like your husband's job is a major source of stress. How feasible is it for him to get another job? My husband is in the military, so that isn't going to happen for us! Can you afford a few hours of childcare a week for the kids? When my oldest was two I had him enrolled in a daycare as a drop-in. I mostly used it for my doctor's appts., but I usually ended up putting him in for three or four hours every other week or so, just to give myself a break. It helped immensely. Something like that would depend on your kids' temperaments. My oldest was extremely flexible, he didn't mind the break in routine. I don't know if my middle child would handle that as well which is why I haven't done it with him yet.
My solution for myself is to stick it out for now. I'm putting my 3yo in half-day preschool for three or four days in the fall. I have a playgroup that we go to, just to get us out of the house, and I try to stay moving as much as possible. It is hard. I actually started browsing want ads a few months ago, I was so fed up. It doesn't have to be all or nothing, though. Maybe you can find an arrangement that will give you a bit of a break but still allow you to be at home with your kids most of the time.