I think my cat's in labor...

Our cat Pixie is due to have kittens on Monday, but I think she's laboring already.  She hasn't eaten today, she's slept more than usual, when she is awake she's wandering around meowing and won't leave our sides. I laid down on my bed for a nap this afternoon and she came and laid right next to me...highly unusual.  The kittens have been really active as well; she laid on the living room floor this afternoon and we could see them writhing around in her belly. 

I've helped deliver kittens before so I know when delivery is imminent...I just don't know how to recognize the signs of early labor.

Anyone got any advice?