Overheating with intermittent A/C

Vehicle began to cycle out on the A/C, would go warm then cool then back to warm, thought maybe the serpentine belt was not running well so I checked that out. The car then began to overheat, so I thought maybe the water pump was going bad, maybe it was not turning causing the A/C issue. The seep hole is not leaking on it and the belt is not screaming. Verified it is all running okay. Had some loss of power and delay in get up and go, previously replaced the ETC and flashed and thought the accelerator pedal was not working properly. Overheating started today, and I had not smelled coolant before today. Let car cool then started it again with the radiator cap off. The reservoir was full but the radiator was low. I carefully added antifreeze/coolant and could verify there was air in the line, revved it up a bit and filled until full. Have not driven it since, but it ran at the proper temperature for a while and the A/C ran just fine. I cannot find a leak anywhere. How did air get in? Does the coolant run to the transmission? If so, there may be a leak back there. Also while on the way home, I turned on the heat hoping it would help cool, it did but nearly cooked us on the way. I figure maybe the thermostat is sticking, but where is the coolant going? No there is no tell tale white smoke coming out and it is definitely not leaking into the motor. Seems to be running okay now and the loss of power is gone, but I am sure I will have the issue again.