Sounds very familiar. I have a dd that just turned 4 and ds is 7 mos. I would have days like you as well. It is different haveing 2 kids instead of one. I had issues wih dd and yo are doing great by choosing your battles. I also had to give up nap/rest time for her. This is her second year of preschool and it was great when she went back this year. Take each day as a freash start. One thing I did with dd is when I did/do "loose it" I would sit down with her and we would have a little talk and I would calmly tell her I was sorry for yelling and hurting her feelings, I would explain that Mommy is tired and I need her help as a big sister to look after brother, help set the table etc and that would make her feel better. We would end or talk with a hug and a kiss and lots of love yous and things started to get better. Godd luck, keep up the good work.