First of all, you should cut yourself some slack. No mother is perfect - and you don't have to be, either.
I am working on my PhD in Education, so have taken LOTS of classes about children, psychology, etc. One of the most powerful things that an instructor ever said to me (and I remember this VERY clearly because I was pregnant at the time and worried about everything) is that research consistently shows that all a parent has to be is "pretty good" for a child to turn out wonderfully. There is no added benefit for a child if a parent is "perfect."
We're all going to mess up. I do it consistently with my child, who's now almost 8. I am a single parent with a lot of stress and a pretty short fuse. And she is perhaps actually a better child for it. She knows that there are times when she should back off. She has a healthy respect for people's boundaries. She is also more polite than many children. I think part of this comes from having a mother who will say, "No. You are really bugging me," and who has feelings around her.
That said, I also think that it would be a really good idea for you to get any and all the help you need and or want. You deserve a break. And you may be right that this could help you with your level of frustration, etc. I know that I, for one, could not be a stay at home mom. It's too hard. And I know that I like my daughter a LOT more after she and I have some distance every now and then. I've noticed that if she spends time out and about with family or friends or at school, the time that I spend with her is much less fraught with frustration and that I am much slower to anger.
If it's *really* bothering you how you are feeling, etc. I would recommend visiting a therapist who can help you work through some of your feelings about these incidents. You are under a lot of stress, as well. Raising two kids is not easy, especially when one of them is in that toddler stage of new independence. Your therapist may also help you work through ways of coping with that stress or in finding new ways to diffuse your anger. But, I would guess that simply getting some distance will be enough to allow you to handle your frustrations.
Finally, I'll put this out there, because many people have made me feel really awful and guilty over the years about my certain knowledge that I can not be a stay at home mom - and though I know (or at least hope) that no one will make you feel bad on this website, it's at least important to note. Taking time off from your children does not make you a bad mother. Being frustrated with your children does not make you a bad mother. We are not all, nor should we be, June Cleaver. Your children have a mother who is doing what is best for herself, which is also the best for them.
Good luck!