coolant system problem?????

[that_guy5]

i got a 98 civic with a y7 stock except intake but anyways this dam car has been losin coolant and overheating about every 2-3 days. the needle starts to go up i stop let it cool and service it back up. the weird thing is that the overflow tank is full but not the radiator i see no coolant puddles or any leakege at all. i changed the thermostat, upper and lower radiator hoses, thermostat housing, cap and fan works too. i taken it to the mech. to do a pressure check and checks fine. some have told me its the head gasket but no milky haze in oil or anything in oil, no white smoke or anything like that it runs normal except for the overheating prob. im stumped i just want to get the car fixed cause im planin to drive it back to cali from va and dont want to get stuck somewhere but does anyone have any ideas??? can u guys help me out plz?? thanks