Actually I have to admit, I am undergoing the same situation. I have a 11 months old daughter and I want to sleep all the time.
I got a complete checkup and there is nothing wrong with me as per the doctor. There is a psychological reason behind all this. You are actually tired of being in a state of consciousness and wakefulness all the time.
You must have noticed that you probably have never had a whole night's sleep. Your daughter would wake up at least once for some reason. This creates a situation where you feel you have not had enough rest even though you have slept for 12 hours.
So the only thing you can do here is that, make a conscious effort to do things on time. Make sure you go to sleep early, preferably at the time when your daughter goes to sleep and then also have some rest whenever she goes to sleep. This will increase your rest time and would help in recovering your sleep.