Running hot when stopped

For the past six or more months my car has been running hot but only when stopped. We changed the thermostat in it because the diagnostic test said that is what it was. It ran fine for a little bit. Now it i's back to doing the same. I never see any fluids under the car when stopped like its leaking but we are having to add fluids every three to four days. There is also a smell like burning fluids and some days thick (some days nothing) white smoke from the tail pipe. We have had people mention it needs a radiator flush maybe a new water pump or it may be blown head gasket. Any advice is greatly appreciated.