You sound so overwhelmed.
I won't pretend I have answers - I only have a nearly 2 year old - but, do you have time for some reading?
One thing that comes to mind is PET - at its heart is better, more open communication within families. (some PET articles from Kelly in here)
One book I read that was very interesting (and in a similiar vein) was "How to talk so kids will listen, and listen so kids will talk"

But... I'm guessing you probably don't have a lot of time to curl up with a book. For what it's worth, I don't think you've screwed up, I think you're just in a difficult place right now. Hopefully something will change that.