Patience is a vertue

Well, I am pregnant again. Now with a 3 year old running around. The first time being pregnant was well FUN in a sort of way. Now with a 3 year old running around I find my patience is NOT as good as is used to be. I don't know if it is just hormonal or what ; but poor Sonia and Rich sometimes because they get the brunt of my impatience. I find myself getting more aggrevated at Sonia and saying things that I really don't mean. I do appologize to her but I know that she does not understand why mommy is different I guess.
Please any suggestions would be helpful.
Thanks