Hi N.,
I recently had my fifth child. My oldest is 7, so I know what you mean about feeling like going insane! Also, I spent 6 weeks this summer as a single mom, right after my baby was born, while my husband worked out of state.
First of all, I told my kids that it was not good for the baby in my belly to hear me yelling. It scared him/her. They agreed that it was unfair to the unborn child. They have a connection to their sibling, even before he is born. So, I often reminded them of this when I felt myself getting angry. Patience seems to be so scarce when you are pregnant!
Try WHISPERING every time you want to yell and feel yourself getting worked up. It can be just as effective with the older kids. They may be so shocked that they listen and respond!
When my husband was gone, I was worried about how I would maintain control. In the end, I had great control and things got messed up when he got back! But the first week was rough. I felt like I was a mean mom that whole week and had to be on them every minute. I couldn't let things get too far out of control. Soon, they realized there was ONE authoritiy figure and things went much more smoothly. Decide what your limits are and STICK TO THEM. Do not budge one inch. BE CONSISTENT. I know it is hard and you hear this all the time, but I can tell you it really makes a difference. I have to be consistent to maintain sanity with 5 little ones. People often comment on their good behavior, so it must be working!
Good luck! I hope things start looking up for you!
T.