Anger and how to deal with it?

Something is not going so well as it should be - I feel like I'm perpetually losing my temper and I'm too frustrated to try to figure out the root of my problem. I keep saying I don't know what's wrong with me. It's tempting to think I'm just not cut out for this, I'm no good, I'm an awful parent. I felt so together until Morgan got mobile - well, mostly. Now I'm just mad at them both all of the time, always picking at things that don't matter and flying off the handle when they do normal kid stuff.

I managed to break the safety gate at the top of the stairs today. Jenna had been winding me up over really minor stuff and I can see now that she wasn't doing it on purpose. The urge to hit her was just so strong. I'm really ashamed of myself, I had a proper toddler tantrum and threw the washing I was carrying on the floor and kicked the baby gate. It fell off its hinges and then Morgan and Jenna were crying and I was screaming at them (if only I could take that back and go hit a pillow in private). What can you do when you lose it so badly? Well I had to ask myself what I'd want Jenna to do if she'd just done that... I said sorry and explained why I'd handled it wrongly and what I should have done. I asked her to forgive me, and hugged them both. I tried to fix the gate and then said that Daddy would help me do it later.

We only just got out of the house this morning without someone being smacked. I never thought I could come that close. Thinking about it now I can see that really I only wanted to hit her BECAUSE I knew it was wrong. In my anger I just wanted to lash out, do something terrible. Is this what my own experience of being disciplined has taught me? Has my adult life done nothing to take away the desire to act bad because I feel out of control and doing something naughty gives me the control back? What a failure.