Pruners we all can feel like that. I pride myself on being a "good mum" because i don't do/try not to say the crap stuff my dad /did/said to me as a child/teenager.
But i don't always manage it. My ds1 and i are very very close and i think the world of him most of the time. However i did something really truly awful last week We had been to dh's uncles funeral,my dad was awaiting test results and i had PMT.
We had cross words and i flipped and threw him out and . Thats the kinda twisted evil thing my dad did to me. I knew that he would go straight to his gf's family and stay there or i would have gone after him. He and i got a huge fright and we talked/said sorry which is way different to how my dad would have done things,so in that respect i am not my father.
It's not the same as what you are going through right now with your ds but no matter how badly you feel you are doing as a parent,the fact that you are thinking about it and you realise it shows you are a good mum and things will improve and it does get easier i promise.
I also have days when i wish the lot of em would piss off and give me some peace but i do a hard job and i am allowed to feel like that sometimes!!!