1997 Ford Contour coolant backing up into the reservoir

Recently I have changed the thermostat, bypass hose, a heater hose and flushed my coolant. My car is still leaking fluid, but I don't see it coming from any where but the reservoir thru the pop-off valve in the cap. The level in the reservoir is fine but after I run the car for a while it backs it all up in to the reservoir. Could this be because the water pump isn't working properly? Plus I have looked for the water pump and cannot locate it on this particular vehicle, so I can't check the weep hole, could you please point it out for me and how to get to it? Thanks, Randy