Zero Patience.

I am 8 weeks today, with number three. My two daughters are 8 1/2 yo and 5 1/2 yo. The past week, I've realized that I have no patience with them whatsoever. It seems like everything They do irritates me. And I feel terrible. We haven't told the girls that I'm pregnant yet. Please tell me that I am not the only one feeling like this? If any of you have dealt with this, what did you do to help?