Overheating

Last week I bought the car listed above it is the Limited Edition. The day I went to test drive it, it started to over heating about five miles down the road. I drove back to the dealer and he added some coolant then explained it was low from sitting. Afterwards it drove fine. I ended up going back a few days later to get it. It drove fine for four more days before it started over heating again. It happened on my way home from work. The twenty five mile highway trip was fine. I then have a ten minute city commute. When I got home I placed the car in park and began grabbing my belongings. I noticed the heat turn ice cold (Michigan weather) so I shut it off and check my temp gauge. It was below red, I quickly shut the car off and checked the coolant. It was over the fill line so I let it sit over night and drove to the gas station the next morning. It drove fine there, the heat was even working. When I was I put it in park again it began to over heat. I drove home with the heat on high. I did some research and bled the system. I checked for white smoke, it's not my head gasket. I checked for pressure in my hose. It is not that. I checked my relays. It is not that. I even replaced my cap just to be safe. My next step is my thermostat or my water pump. Also my reservoir was full to the cap. So when I bled the system I got it back down to the fill line. What worried me was the heat blowing cold air. What do you guys think? I do not want to find out I wasted my money just to put more money into it. Thanks for reading, I know it is long.