With 7 kiddos at home, is it possible that the only time you get to sit down is in your car? I have 4 little kiddos and I naturally only slept 3 or 4 hours a night for years until it caught up with me and I had to change my lifestyle to fit in at least 6 hours. My house is a whole lot messier but I feel tons better.
There are many reasons you could be tired. They run the gamut from adrenal shut down to sleep apnea, poor diet, lack of exercise, nearing the hormonal changes that go with menopause, even scary things like crones disease or lupus.... But only your doctor can tell for sure so you do need to get a physical and some blood work done.
Until you can get to the doctor, do you have the ability to take a mini-vacation for a whole day/night? I have a friend who always seems to be up on the latest new age health fads and her latest kick is sleep therapy. She recommended I take a 24 hour sleep vacation and get a babysitter so I could lay in bed for one whole day/night.... That just isn't possible for me although it sounds heavenly. She showed me some pretty cool studies that show your body is able to hit the magic reset button when you get to about 15 hours of sleep where your nervous system can regulate out of whack hormones and brain chemicals to natural levels.....
But again, your doctor will be able to test you for whatever is causing your fatigue.