You haven't it just feels like it. Seriously, there are challenges that sometimes feel overwhelming for everyone. I dread the thought of teenagers as I am struggling with Miss 3.5 going on 13. We have had similiar issues with her behaviour as she is outright defiant, clearly misbehaving and hitting etc when she knows it is not on. She also crys etc at childcare and is having issues sleeping (she has never been great). I wonder if there is a stage/adjustment they go through at this age? It seems to be a very common comment amongst my MG.
I had a big bawl at DH a few weeks ago as it was all getting too much, so you are not on your own.
I did some reading and found some alternative options that seem to have helped in regards to DD1. But most of all I have cut myself some slack. Trying really hard to acknowledge what is working and be a little kinder to myself. Also trying to be more consistent/calm rather than as reactive (I was letting the sleep deprivation etc really wind me up). Not much help really am I!
Hang in there - your 'job' is to be tested and challenged and put up the boundaries and rules for your kids. It is a pretty thankless task and often takes some time to see the goods! xxxx