2001 Ford Ranger Freeze Plug(s)?

I was changing my thermostat last night and when I was adding the new coolant to the radiator, I noticed that there was coolant leaking from or what looked like the rear of the engine. I got underneath, but was unable to actually see where the coolant was coming from. I do know, however, that it was not leaking from any main hoses, the thermostat area or the water pump. I was informed that it might be leaking due to a freeze plug. Now, on my truck, is there more than one freeze plug? If so where are they located and how hard is it to replace / repair? In addition, would it even be the freeze plug that would cause this? (Also, there is NO water in the oil and there is no smoke coming out the tail pipe when it is on; just a flow of coolant.)