R.,
Leave the house! I am guessing that since you are a SAHM, you have a husband around (someone's got to pay the bills, right??). When he comes home, or is off on a weekend, leave. Go anywhere. See a movie alone, sit in a corner of the library and page through a magazine, get your hair cut. It's necessary for sanity to not be surrounded every minute of every day for years on end with small chattering people.
I know a lot of husbands don't love this, but too bad. I bet he doesn't take them all with him when he goes to the barbershop, or to Home Depot to pick something up, etc.
My husband and I have worked out a system. On Saturday mornings, he sleeps in as late as he wants, and I get up with our son. Sundays, it's my turn. I sleep in as late as I want while he gets up with the little guy, then I go grocery shopping. So, from bedtime Saturday night, until I get home from the food store around 11 or so on Sunday morning, I am off duty! We also both get to go out socially whenever wefeel like it, no questions asked. My playgroup does a Mom's night out each month, and I go to that, or to meet a friend to see a movie and have dinner, and he takes on our son for the evening, no questions, no complaints. My husband bowls once a week, and that's his night out. I don't plan anything that interferes with his bowling night.
We are all parents, but parents aren't ALL we are. You are still a wife, a friend, a woman of your own. You need to have the opportunity to nurture all of your roles in order to feel good about the whole person. It's so easy for Mommy to drown out everything else, but when they get older and you look around an empty nest, who will you be? What will you have if you let all of your interests and hobbies, and outside relationships die off?
Go out and have some fun!