I just wanted to send you a hug too and let you know that you are definitely not alone. I agree with the pp about trying to watch what the kids eat. I haven't followed any book but noticed how much packaged/prepared stuff we were using and just tried to get back to basics with more fruit/vege and more homemade stuff. Interestingly we have also slowed down a bit and spent more time hanging about rather than racing doing things on our home days and it has helped a bit. My younger DD has turned things up a notch too and is way more competitive with the eldest and I also think this has contributed to the angst. She has been way more confrontational, physically challenging DD1 and this change has needed some negotiating between them. I have also been sending them to run laps around the washing line and bouncing competitons on the tramp just to burn up some excess energy.
Can you get any time out? I find it hard as I get worn out with work and then trying to make sure everyone has enough time/fun with me and all the jobs get done when we are home and often forget I need some love too!