Sleep!

I need sleep! For months after my surgery I struggled with insomina, but after Grady was born it seemed to ease up quite a bit. The strange thing was that I could still function, I was a little sleepy, but I didn't feel like a zombie. However, once I could sleep again I have been suffering from sever fatigue :( It is as if I can not ever get enough sleep; I can sleep 10-12 hrs at night & take a 2 hour nap & still not be able to function. I feel run down and can hardly function, let alone be a good wife and mom. It's not just that I'm tired, my body is weak, my mind is frazzled and I have no motivation to do normal things. I've tried exercising, it does wonders for my mind and really gives me a better outlook on things, but once I get home from the gym or walking etc... I can hardle manage to stay awake to fix lunch- I feel like I just ran a marathon.
I've talked to the Dr. about it and he contributes it to my body trying to readjust and my cancer levels/blood work being all out of wack! This is the 3rd night where I haven't been able to sleep. I have gotten quite a few things done during these night hours, like painting, laundry, worked on some pictures, etc...But come morning I can hardly get out of the bed & crawl back in the 1st chance I get.
AGHHH! I just want to be able to lay down and fall asleep, to stay asleep and to wake feeling rested. I know I am a busy woman, I have 4 kids, but...I just want to feel normal again!