leaks,Just noticed a huge oil leak trailing my car. It seems to be coming from below the engine. I recently had my oil changed a month

My oil leak is very large , I lost a quart of oil in a mile radius. The oil seems to be coming from below the engine between the front tires. I noticed the oil leaking behind my car as I pulled into my driveway. The strange thing is I turned the car on and laid down under it and it didn't drip , it only seems to leak as I'm driving. But it's a huge amount of oil. A month ago I had my oil changed at Walmart they had told me I had no oil in the car , after they put new oil in I checked it regularly for the last month , it didn't lose a drop. Now in the last mile I lost a quart an