Pontiac Repair: Coolant, losing coolant, worst case scenario

Question
I have a 95 Grand Prix 3.1 engine.I keep losing coolant, i've checked the oil, none there, can't seem to find any leaks.I changed the thermostat, when I first started getting a low coolant light and high temperature light. Can you tell me where the coolant is possibly going.
Thanks
Dave

Answer
this is not a good situation.if there are no leaks and the temp.keeps trying to climb more than likely the coolant is leaking into the cylinder while the engine is running and burning off with the fuel.i have seen this and it doesnt usually do it until the car warms up.the head gasket may be the cause but worst case scenario is a cracked head.good luck