I think I get too angry/irritated sometimes with ds, and feel really ashamed when I do. There are times when he is being challenging (won't put on his diaper, etc.), but most times I find it's because I want to do something, and he isn't cooperating. I find it helpful to often just surrender at those moments.
However, I know that isn't always helpful, or doable. There are 3 things that I have identified that make me much more irritable: Lack of sleep, not enough water/not eating right, and not getting enough time to myself. When I am deficient in any of these areas, I am much more likely to get angry with ds throughout the day.
Maybe check those things, and see if there are any areas in which you can get more of them for yourself. If you think it is runs deeper than these things, then I second the suggestion of seeing a counselor or therapist. I have done this in the past, and she had some really good suggestions for alternative ways to deal with anger.
And please don't be too hard on yourself. You have the toughest, most demanding job, and like the last poster said, just the fact that you are conscious of this as an issue, and that you want to make a change, means that you are a thoughtful, sensitive, loving mom.