Check your drain plug, your oil filter and make sure you don't have a crack in the oil pan. The oil pan gasket might have gone out as well. After that, check your valve cover gasket. Finally, if you still don't see anything, fill up with fresh oil, let the car idle and use a flashlight and you will see where it is leaking. If it leaked and nothing was touched, it'll leak again from the same spot. You can find out that way. Good luck with it.
