...there's alot of dirt and oil under the oil pan?

 

Oil is leaking. Look up at the engine from underneath and look for the highest spot that oil is. That's where it's leaking.

 

get some simple green and clean it really well, try to remove all traces of oil and grease. Then check it every few days and the leak will appear. It's common to get some spray on the oil pan from the front timing seal on the crank, but if you don;t clean the little mist every now and then, it can end up looking a lot worse than it is.

 

+1 Ryan

My 2000 engine is almost new and does the same thing, doesnt lose oil just mists it back a little sometimes.