1997 Pontiac Sunfire over heating

Car over heats every 2-3 weeks, thermatat changed, water pump changed, no oil in cooling system, how else to check for bad head gaskit, no smoke through exhaust, car also in accident 2 yrs ago, went under SUV. Electic fan seems to be working. No leaks under car car to be seen, water level goes down and car over heats, only water seen then is out of overflow bottle