1996 Other Nissan Models Water pump/radiator problem?

I have a 1996 NISSAN QUEST that has recently been experiencing some coolant leakage problems and trying to find what the source can be. In addition even when I refill it (radiator) and this is usually every few days and I turn the heater on, it may blow hot air but it may also come out cool for a while. It does work better when I am accelerating, especially on a highway. Can u tell me what may be happening here? Thanks