I feel for you titfer, and I think you're doing the right thing by getting your frustrations out here.
You're being brave to admit to feeling fed up with it all at the moment. But why should we have to pretend like this is always the most wonderful, rewarding job in the world all the time? It's f*cking hard work, with no let-up and there are no workplaces where your co-workers or boss could hit you, scream at you or poo on you.
Agree that you need a break. It could make all the difference. I have a 3 yo and a 1 yo and DD1 has been very demanding at times. I have also been in your position and reacted the same way out of anger, frustration and desperation.
My DH was witness to it all, which made it feel worse. However, he never said a word about it, just calmly started making arrangements to be around and help out a bit more. He booked me a weekend away and arranged some days of parental leave so that he can be more hands on with the girls.
The best bit of going away (only for 2 nights but felt like luxury... our 2 are also poor sleepers, so exhaustion has to be part of the problem too) was that when I returned DD1 seemed to realise that I could no longer be taken for granted. There were two months between it all crashing down for me and me going away, so she can't have perceived the two to have been related, but still she has been different, and much more loving to me since then. Better at listening, better at saying sorry when things go wrong.
Could you get a night away ?(I know this would mean making arrangements for feeding your youngest, but could be worth it...) Being well-rested (or at least better rested) can make the world of difference to how you feel.