My car has overheated and I tried to fill up radiator but it just never fills up?

My car has overheated and I tried to fill up radiator but it just never fills up, where is it going? I can say the heater hasn't worked and we recently replaced the thermostat? It's not a hose, checked all of those?? I have limited funds so I really could use some brainstorming to help me with fixing it my self?