At that age, they really start showing more personality and it's easier for even a sane person to attribute motives to them that are more complex than what is really there.
I've had my moments.
What is working for me, because I am sleep deprived and I'm not getting any soon:
1. Sleep. If possible. The full eight or nine hours. If that's missing, then something to compensate.
2. Magnesium supplements changed my life. Wow. It's linked to depression and nervousness. It's depleted easily by calcium/dairy, coffee, alcohol, stress... I'm not a wino but between a nightly glass, tons of dairy and coffee, and stress, I was probably totally depleted.
3. Yogic breathing. Even if I look like a nutcase I shut my eyes and breathe into my stomach, out the nose, count to five... until I can deal with them calmly. Even if I have to hold their wrists while doing it, LOL!
4. Cognitive behavior therapy workbook. Changing my automatic thoughts (e.g. "Why is she doing this to me" changed to "I'm the mom. I can do this.") is helping a lot.
I have a lot of stress but I've been yelling a lot less even though I'm going through a separation with my husband, have an almost-four-year-old and an 18-month-old.
I don't find eating helps me so much unless I'm really hungry.
Sometimes it's so hard to be the mom we want to be!