I change the motor oil in my car this week after a little more than 3000 miles, however, I notice and this is the first time that happen, that when I was putting the used oil into containers to recycle, I only fill half of a empty qt of oil, my car does not leak oil (there is no sign of oil where I park my car in the house or at work, since I park in the same place), and my car does not burn oil either, what can be causing my car to loose oil? Any help or advice will be appreciated.

Thank you.