nappies, don't know you personally (though you seem to have freaking huge numbers who do know you and love you here)
Just wanted to say what everyone else has said - that I so empathize, and mine aren't 3 under 5.
You are obv v smart - though I know that makes no diff to how shite one can feel - but you've hit nail on head I think, about what will start to make you feel better. Aiming low is good, if aiming high is only going to reinforce general feeling of shiteness.
I've felt at times as tho what I am like with DS and dd is tantamount to emotional abuse.
Suddenly, like a revelation, I realized that the only problem, in truth, was my guilt - that was the thing that was causing the NEXT outburst.
In combo with getting out and about, a bit more involved in other things etc, I've managed to drop the guilt, quite a bit. Involved being honest with dp, and close RL friends that actually know my kids. And trying hard to remember how I felt as a child, and the things that really upset me (they weren't being shouted at, they were about betrayal, being lied to, being told that I was ungrateful etc)
And I got far enough away from the kids to see them as the babies they really are (this involved looking at photos of them as babies, bizarrely. A photo involves a layer of distance that can be quite useful)
Recently, everything feels completely different. I look at them and don't see them as problems. My heart turns over again.
I've ABSOLUTELY no doubt that this will all change tomorrow. But the fact that I've been able to do it once makes me feel I will be able to do it again.