I noticed a tiny hole in my drywall and a water stain on the ceiling and a constant drip from the ceiling, even when the shower is not in use. I did a test by pouring water down the shower drain, and it immediately went through to below. Also, my shower head and leaks constantly. Any help to what I can do to solve this, and what is going on here? Thank you

You have two problems. Let's work on the drainage first. Cut a square section of ceiling out and save it. (You will use it as a patch later.)
Now watch the drain and trap while someone pours water down the drain. Take a wad of TP and tell me the highest point that you pick up moisture. Let me know , Tom