99 Mitsubishi Sport had no oil - where did it go?

My car runs great, but one night I started my car up and it was ticking so loud. I checked my oil, no oil on the stick. Added about 3 quarts. I took it to a mechanic, he changed the oil and filter. He also checked for leaks, can not find a leak anywhere. My car does not smoke. The only thing I noticed is that my exhaust pipe drips a lot of water when first started up. Prior to my oil change, the oil has not been changed in 6 months, could this be the reason. :Roll: