Water noise coming from heater and rising temperature?

I can keep hearing water gushing around under the bonnet from inside the car through the heater at the front..The temperature also keeps going up & yesterday i had steam coming off the top of the bonnet when in heavy traffic.Also the fuel consumption has not been good of late.
Ive got a 1995 1.4ls Vauxhall Astra
Have been filling the expansion tank up with water as it keeps dropping but can't see any leaks.Added some coolent also but think i might need to add some more.Does it sound like the head gasket has gone or is it the radiator??.Please keep the replies simple as i'm a Lady & understand a basic car related things!!