All of my oil has leaked out of my Vue!!?

What is your question?

I was driving my Vue for the first time in about a week (my wife drives it all week) and noticed it had started to "tick" while stopped at the ATM. When I got home I immediately checked the oil and it was empty. I looked around my driveway and there was oil on the driveway from where it sat the last 24 hours. There is also a "milky" substance on the oil cal/ dipstick. My coolant level is norml so I don't believe it's the head gasket and I JUST replaced the PCV valve 9 months ago due to a similar situation. Does anyone know what this could be and how pricy it is to fix?? PLEASE HELP!