I have a '96 Chevy Lumina car. I need to add antifreeze to the reserve bottle every other day, however, there is not leakage on the ground. I have had two pressure checks and both places indicated that they could not find anything wrong? Any feedback is welcomed.

Have someone add coolant leak dye to the cooling system and then pay particular attention to the area at the rear of the intake. That gasket is prone to seepage. That seepage is difficult to find on pressure testing. Frequently it can leak only once the engine has cooled off, though sometimes will only leak when warmed up.
You may even need to drive the car for long enough for the dye to show.

Have both your intake and/or head gaskets checked. In all likelihood, you have an internal leak; dye is recommended although won't always be apparent if the leak is internal