Intermittent overheating and coolant loss

Been having an odd issue with my vehicle listed above. This is going to be lengthy, as there is a lot to explain. Some time ago the car was overheating. Took it to my local guy who typically is very good and won't do unnecessary repairs. After some diagnosing, he felt it was the radiator, so I had him replace it. Picked the car up, drove a couple miles to my folks' place, and when I left there a short time later, the car overheated again. Took it back and the garage said that there did not seem to be an exchange of coolant, so they replaced the thermostat. Continued to have issues and they felt it was the head gasket. Now, it doesn't appear that coolant is leaking into the motor oil, and we did not have the cash to do a head gasket repair, so we opted to have him use Blue Devil gasket sealant. Seemed to work and the car ran well for some time but then overheated again. We put antifreeze in it, as it appeared that the car was losing coolant. The car set for a day and when I took it to a different garage to look at it, it did not overheat while driving it there. That mechanic said it was the head gasket and that he had put a gallon of antifreeze into the car. He also said that it was leaking coolant on the garage floor, which I didn't believe because we haven't seen a bit of antifreeze on the ground or driveway. I took the car home and proceeded to drive it for several weeks without any overheating. I added coolant once, but not because it overheated, only because it appeared to be losing coolant. The other day, I checked the reservoir and it was empty, so I put coolant in to just over the "full" line. It overheated again. Running the heat kept it manageable, but still running pretty hot. We were away for a few days and I took it out today. Before doing so, I filled the coolant reservoir just over the fill line and took it to the store. Again, it overheated. I checked the reservoir at the store and it was still full. When I left the store, I drove the car for about 20 minutes and it didn't overheat. When I got home, the coolant reservoir was empty. So, that's where I'm at. Not sure what's causing the car to lose coolant, and I'm fine continuing to add coolant, until I'm in a place where I can afford another vehicle or this one just stops running. Thank you for reading this long explanation. Curious as to what your thoughts are on this.