M.F.
I quit my job of 5 years in July of last year to stay at home with my then 2 yr old and 4 mo old. I have to say that I spent much of the first 6 months or so at home wishing I hadn't quit my job, and have thought it again several times since then! Staying home with kids is not something I thought I'd ever, ever, do. However, I'm beginning to realize the rewards of it (a whole year later!).
I'm not one of those sweet and emotional mamas who love every minute of home life and gush about my "darling little angels." When you're home with them all day you realize that they're darling and angelic about half the time -- if you're lucky. The other half the time you'll catch yourself thinking "I brought you into this world...." I really struggled with the fact that I didn't simply LOVE staying at home like so many other SAHMs seem to. Do I LOVE my kids? YES! Did I want to spend every waking minute with them? NO. Like the other moms said, definitely find a MOPS group or something for support/playdates. There will likely be a mom or two that you click with. If you can afford it, enroll your daughter in some sort of activity (gymnastics, dance, Kindermusik, Young Rembrandts, etc) or a mother's day out program. She's at the age where friends are important and if she's used to childcare with other children around, she'll likely be missing that sort of stimulation. Check the story time schedule at your local library for something fun to do that both kids will enjoy. If there's a story time specifically for kids your son's age, don't feel bad about bringing your "big kid" along. Not only do others do it too, but I've found that my daughter enjoys helping her brother learn all the songs and rhymes as much as he enjoys experiencing them.
Also, from the beginning, keep or get something for yourself. Build rest time or "me" time into your day. While my son was younger and still took a morning nap, I also had my daughter have "room time." He slept, she played, and I got to make some phone calls, work on Bible study or do anything else that I wanted to for at least an hour. Even after the baby dropped his morning nap, I maintained that sacred hour personal time. Afternoon nap isn't enough time to do everything I need to do, so this morning time is really important. I have also realized that the "me" time helps me be less exhausted when my husband comes home. If the kids suck all the life out of me, there's nothing left for him! And speaking of your husband, now is the time for guilt-free date nights. We didn't date much when I was working because we both felt guilty about leaving the kids. Now we have a "swap" with some friends and we go out every other Tuesday. On the weeks where we don't go out together, we rent a movie or play card games one night after the kids go to bed.
Also, I recently joined a gym and wish I'd done it sooner. I had no idea how rejuvenating it could be to spend a full hour doing something totally "grown-up" (the gym has free childcare where the darling little angels are perfectly happy).
If house work is a high priority for you, try to dampen your expectations. It's not often that you'll be able to spend more than 15 to 30 minutes on one task. I began my SAHM life with a lovely looking regimen of a different housecleaning task each day of the week: Monday laundry, Tuesday dusting, Wednesday floors, Thursday bathrooms, Friday was my day "off." Realistically, you need to do a load of laundry every day (but just ONE). And I have to think of dusting one piece of furniture at a time or in 15 minute increments. I vacuum if I think my black sweat pants have a little too much dog hair on them after rolling on the floor in a tickle-fest with my son, and the kitchen floor gets mopped when I can feel my feet sticking to it (which is more often than you'd think). I bought a lot of small baskets and containers to hold toys because it's easier for me and the kids to keep things picked up that way. And I'm just now realizing the joys of having 2 little "helpers" with household chores. My 3 yr old puts the clean silverware away and sets the table for dinner (silverware only). The 20 month old helps load the dishwasher (plastic dishes only) and the two of them are quite a team filling the washing machine and transferring clothes from the washer to the dryer. I had to let go of my ideas for getting things done quickly. House work, with helpers, is painstakingly slow. And I've learned to plan ahead -- it takes 20 minutes to load the car to go anywhere. If we're having company on a Friday night, I have to start cleaning the house (a tiny piece at a time) on Monday in order for everything to be ready by the time guests arrive.
I figured out that where I was in a rush, they were, literally, taking time to smell the roses (have to walk past them on the way to the drive way), learning about different sounds and textures, the differences between cause and effect, heavy and light, squishy and hard, stinky and not-stinky....
Yes, the cycle of never-finished mundane work will get to you. Just know that it gets to all of us. When it does, that's when we order pizza.