Sounds like you could use some 'me' time. A year ago my kids were the ages of yours now, and now I have a baby also. Here are some of the ways I get some 'me' time. 'Me' time is important because it helps you recharge and stay refreshed and be the best mom you can be.
*the kids nap time is my time, I may do a few household things, but otherwise that is when I get on the internet, read a book, maybe take a nap, read my bible, pray, etc.
*some moms reminded me of how important it is to read my bible and pray regularly. Do it every day if possible, or at least 3 times a week. It doesn't need to be for an hour at a time, 10-20 minutes or half an hour will really help you out! Take time for the Lord and he will give you the strength and wisdom you need to make it through your day.
*I let the kids watch 30 min of TV in the morning, that is my time to get things done and not be disturbed.
*go out on a date with your husband, very refreshing
*go out for an evening with some friends and leave your husband home with the kids
*during the day when you need a break, drop the kids off at Playtime +, there is one located at Elm & 101st, behind Arby's & Sonics. Playtime + is a drop in playcenter/daycare.
*Sign the kids up for 1 day a week with an Early Learning Program (Arrow Heights Baptist Church has one) or Mom's Day Out (Grace church has one, as do many others in the area, the Baptist church on Elm & the BA has one) Then you can have part of a day off
*Trade babysitting with a friend, you watch her kids one day and she can watch yours another, I find adding someone else's kid to our house results in my kids playing more and contently
*Take the kids to the mall to play at the play area by JCPenny's
*have a play date - at your house or the other mom's house, then the kids can play and the mom's can talk
*call a friend or relative during the day and talk to them, you'll feel much better when you get off the phone
*After dinner tell your husband you really need a 30 minute break, have him watch the kids and go to your room shut the door and take the break you need
*when I really need a break during the day I'll tell the kids that mommy needs a break or a time-out. I have them play in their rooms and I go to mine for about 20 minutes.
I'd also recommend taking a daily multivitamin, a Vit B complex supplement and an Omega 3 supplement daily and make sure you are getting enough calcium, lack of calcium can result in my having a much harder time staying calm. Talk to your Dr about what vitamins would help.
Hope there are some ideas here that help!