Hi sad&lonely, I can relate to the stresses of family life.

First off, I would say you need to create some boundaries for yourself, to protect you from the noise of a large family. Earplugs, iPod earphones (listen to some soft music around the house), perhaps there is a room you can lock the door and read or get on computer, or watch a soothing movie. Give yourself some sacred space.
This sets a good example for the kids too, they see that squabbling isn't the only way to communicate, they will copy you and have some quiet time.

I know it's hard, but look on the bright side, you have created a large and vibrant family, they probably need a few guidelines to pull them into line, but you can't do that alone. A family counsellor will help by drawing up a few simple rules to create boundaries and re-inforce respect for each other and for yourself. Some people can cope with chaos. I can't, and it sounds like you can't either. Nor should you have to.
HUGSSSS