Water leaking resulting in overheating.

Go to auto zone and buy head gasket fix.

Did you check to see if you have water or anti freeze in the oil? You could have a blown head gasket. This would be why you are adding fluid so quickly. let me know.

Assuming the engine is ok, no leaking head gasket or exhaust problem, you need to know if the radiator fan comes on when the engine reaches 225 degrees. It should also come on when you turn the ac on if the ac works.
Its also possible you have air in the cooling system.

sounds to me that the engine thermostat has failed

REPLACE THE THERMOSTAT AND RADIATOR PRESSURE CAP.IF COOLANT LOW, ADD MORE COOLANT THROUGH COOLANT OVERFLOW UNTIL COOLANT LEVEL IN THE COOLANT OVERFLOW STAY AT FULL COLD MARK.REASON POUR COOLANT THROUGH COOLANT OVERFLOW MOST GM CARS DONT HAVE RADIATOR CAP.WHEN YOU GET COOLANT LEVEL OKAY, CRANK CAR LET IT IDLE UNTIL ENGINE GET HOT BUILD UP PRESSURE THEN TURN OFF CAR.CHECK FOR COOLANTS LEAKS AT THE RADIATOR HOSES,CHECK FOR LEAKS AT THE RADIATOR, CHECK FOR LEAKS AT WATER PUMP WEEP HOLE IF YOU SEE COOLANT LEAKING FROM WEEP HOLE REPLACE WATER PUMP. IF CAR OVERHEATING WHILE IDLING YOUR COOLING FANS NOT WORKING CHECK COOLING FANS FUSE AND RELAYS.IF FUSE AND RELAYS OKAY THE ENGINECOOLANT TEMPERATURE SENSOR BAD.

SMOKE UNDER HOOD COULD BE COOLANT LEAK FROM RADIATOR ITSELF OR CHECK FOR LEAKING TOP RADIATOR HOSE AND CHECK FOR LEAKING BOTTOM RADIATOR HOSE.LOOK UNDER THE HOOD IF COOLANT BOILING OUT COOLANT OVERFLOW JUG ENGINE OVERHEATING FROM BAD THERMOSTAT OR BAD WATER PUMP.CHECK FOR COOLANT LEAK AT WATER PUMP WEEP HOLE.IF SO WATER PUMP NEED REPLACING.ADD MORE COOLANT UNTIL LEVEL CORRECT.TRY LOCATE LEAK. IF CAR OVERHEATED AND BOILED IT OUT. SMOKE UNDER THE HOOD CAN ALSO BE CAUSED BY LEAKING VALVE COVERS WHICH CAN BE FIRE HAZARD IF OIL LEAKS ON HOT EXHAUST MANIFOLD.

You are describing a slow coolant leak and the resultant no heat and blockoverheating symptoms. The no heat is because there is insufficient coolant to cycle through the heater core, and the chuggin you describe is the engine indicating serious overheating.
With engine cold, you must add water--not anti-freeze--to the radiator itself, until it reaches the top of the radiator, then start the engine. If you do not have a radiator cap in addition to the overflow bottle (some vehicles don't), you must still add water to the radiator, even if you have to bypass the overflow bottle hose to do it. Add water until no more will go into the radiator. Start engine, let idle until operating temperature is reached. Thermostat should open and a good bit of the water will "sink" into the depth of the radiator. If you have no radiator cap, observe the temperature guage. When it reaches normal operating temp, when the thermostat opens, the temp will drop briefly at first, and you will notice warm air from the heater/defroster.
Once engine is warm and known to be full of water, seal radiator cap and/or system, and let idle for 30 minutes. Use this time to locate the "mystery leak." They can be very hard to find, and some won't leak until after the engine is turned off. During this idle period, observe the vehicle exhaust from the tailpipe as well as looking for actual water leaks: sometimes a bad head gasket can be diagnosed this way; if the exhaust is white and thick like steam, and smells like anit-freeze, you have a more serious problem. It is possible that after the repeated overheating cycles you have endured you may now have both a "mystery leak" and a blown head gasket.
Once leak is located, your next step is to let engine cool completely, drain the water, fix the leak, and then and only then add new antifreeze of the proper rating and ratio recommended by Chevy for your vehicle.
Anytime you drain a cooling system and refill it, it is necessary to check the overflow bottle at least 3 times in the first week after repair to ensure that you have the proper coolant level, and have not either missed another leak or not correctly repaired one. You MUST check it before you drive the vehicle the second time after the first repair attempt because it is normal to need to add more coolant than you added initially after the repair because of air trapped in the cooling system that will only be expelled after the first start/stop heating cycle. If after 1 week of daily normal driving you have only added a little more coolant once, and there are no more problems, you can be very comfortable that you have fixed your car.

I will agree with your uncle and say that you should check the water pump. Start the vehicle and look at the water pump. Most water pumps have a "weep hole". If there is coolant coming out of this hole the water pump is not working properly. If not, and if the temperature has been running normally, you may have fixed the problem when you replaced the cap, if the water pump is good and the temp has been running high, then check the thermostat. Hope this helps and good luck.

First thing you need to do is zero in on where the coolant is leaking out,and where oil is going. Sure sounding like a head gasket, or worse. What engine& mileage?

its under the throttle body near the coil pack