1997 Pontiac Grand Prix Recently Replace Thermostat Because Car Running Hot Had

Recently I replace the thermostat because my car was running hot. Then I had to have the radiator flushed because the previous owner had it clogged with stop leak. a few weeks ago the car became very hot and the low oil level and low coolant lights came on. So I put oil and antifreeze in it. Now it smokes whenever I start it and the low coolant light is alway on. The resivoir tank is full, I'm not sure about the radiator because I can't get the cap off. It starts to run hot after driving about 5-10 mins. There is no heat as well.