Designing Kitchens and Bathrooms - One piece shower stall...

I have a one piece shower stall, that has developed a leak, around the drain trap...It has leaked through to the ceiling on the first floor.. I tested to see if water went in around the edges for the drain trap, and discovered that in one area it did.. So I used a little, "Plummer's Goop",around the the area, that the water actually went in, in the sides, and that worked for a while.. Well, you guessed it, it is leaking again.. I have no idea of the way it is suppose to be installed...I think it should be going, or fitting into a pvc pipe, but again, I do not know this for sure...Luckily, I had not had the ceiling repaired yet...Please tell me if is this a job, I myself can do, or should I hunt for a pro.? Thank you...

Easy D-I-Y job.
You should be able to unscrew the drain counter-clockwise, clean out the old plumber's putty, and place a pencil-sized roll of plumber's putty back under it before tightening it down to re-seal it properly. The putty has to go under the lip of the drain, not around the outside.
The flex in the bottom of the shower when someone is standing in it can contribute to this problem, but that should fix it.
Good Luck!