why does my 2004 camry's c/h gauge keeps running hot, but i still have antifreez on 2004 Toyota Camry

It keeps going all the way to the H position, then if i keep driving it gooes back down to half way, then back to H again. but i am not losing antifreeze until a couple of days later. but not alot. could it be my thermostat or water pump?? thanks so very much

Asked by for the 2004 Toyota Camry