Did you refill the tranny or sit there and cry like a little girl with a skinned knee?
Check the case and see if there is an obvious leak. If the tranny fluid drained out in three weeks, the leak should be obvious.
BTW- your post never actually said you checked with the car running, just that you checked it "again" with the car off.
My money is on the low fluid level. Mine was a little low and did the same thing. Refilled it and no problems.
