I filled my coolant resevoir & within 45 minutes it was empty. Temp started to rise. I can't pinpoint where there may b a leak. Could it be thermostat or wateump possibly???

First you need to pinpoint where the leak is coming from before can give you a diagnosis of your problem.

You don't mention if the coolant loss is while the vehicle sits or is driven. If the loss is occurring while driving, there are two possible causes: 1) Intake manifold is cracked or the gasket leaks. 2) A vacuum control valve has failed and the engine is sucking the coolant into the carburetor or intake manifold.