I go there too. I can comisserate. It usually is on the days that dh is working evenings and sleeps in. I feel like we spend our morning creeping around getting ready to get out so he can rest and our evening falls apart because I've been going it alone for hours and see no break in sight. Zen totally keys in to my mood which usually means her neediness increases. It's hard when your the only one on the parenting force who's reporting for duty. I find that when we have a stretch like that it helps to spend some time at a friend's house so dd can play with a buddy and I can have a little break to visit with his or her mommy. Sometimes I invite another mother over for supper so she can play with the kids while I fix dinner. It seems to lighten the load and keep me sane. Do you have family near you? Families are usually pretty good about picking up some slack if you let them.
You are a good mommy. Even good mommies have bad days and act like jacka$$e$ from time to time. I'm sure of it. I usually try to explain to Zen that I'm in a grumpy mood and it has nothing to do with her, I'm just tired. I also like to make use of bath time. If I give dd a bath I can read while she splashes around and then she can play nearby while I get mine and I can try to relax a little again. I guess with two that would prove more challenging. I do admire those of you with more than one child. I have my hands full with one.