Have your cylinder head gasket replaced ASAP. I'm quite sure that's the source of your problem.
+1 on cylinder head gasket. Get it checked by a reputable shop as soon as possible. baka lumala pa ang problema.
baka mag sharon cuneta yan engine.. mag tubig at langis.. pa check mo na agad bago ka pa abutin ng overheat. or baka meron lang portion ng gasket na may leak pa try mo pa check ang higpit ng mga bolts
better have the head checked narin by a machine shop kung derecho pa sya.
most likely the headgasket... pop your hood and take a look at it...