Coolant was leaking to the point of overheating?

I have the vehicle listed above with a 2.4i.

Coolant was leaking to the point of overheating. Changed water pump, timing belt, coolant reservoir, upper radiator hose and overflow hose. The car is still leaking coolant, but no longer overheating. I let it sit a few days to wait for the closest shop (the same shop that did all the repairs) to open. I checked the coolant level before starting it, it was low, I turned the coolant cap and air came out, but the level returned to the max level as the coolant came back into the reservoir. The shop is about a half a mile, I checked the level as soon as I got there, and it is low again. I don’t know much of anything about cars, I do know now the previous owner did not take care of it, but at the time of purchase, the codes had to be reset as nothing was illuminated so I purchased in good faith. It’s been a nightmare. Any ideas what could be causing this issue? Or where to look next? The shop suggested a possible head gasket? But, there’s no smoke coming, rough drive or anything else. It’s just losing coolant! Please help! Thanks in advance.