'97 Coolant Problems

I have a 1997 Mazda 626 4-Cylinder, Manual, with 160k miles. Yesterday, after a 200 mile drive, my engine light came on. I let the engine cool and checked all my fluid levels. There was no antifreeze left in the system. I refilled it, and can't see any visible leaks. Sitting idle for a while, there is a fair amount of liquid coming out of the exhaust. The light stayed on after refilling it, not sure how to reset it.

Any ideas as to what my coolant loss could be?