Coolant leaking onto ground

Okay, first I replaced thermostat and radiator and made sure fan works everything was fine for about two weeks. Then I noticed car overheating again my overflow reservoir was empty and my radiator was low so I filled it. I jacked it up and let it idle and noticed a major steady drip about halfway under the car on passenger side next to middle of right tire. It is not near the firewall my heater hoses are not leaking and radiator hose is not leaking nor my radiator. But the leaks coming from the side of the seem of that large piece of metal up under there and I do not know what it is and cannot actually see where water or antifreeze is escaping. Please tell me what it is I am looking at and what do I have to do to stop that leak? Thanks.
Kitty