She's still awake

I wish my baby was asleep. She'll go silent in her room for two or three minutes, and right when I think I'm home free she starts screeching. Granted, she gave me the gift of a three hour nap today, but I figured she was catching up on last night--when she stayed up 2 1/2 hours past bedtime. I like to blame her weird sleeping changes on getting new teeth, but could it be that she's just messing with me? There seems to be method in her madness.