Umm, there's a walkthrough .txt for it, and a sticky walkthrough on my Discrod's spoilers channel. But my guesses would be that you either missed the receipt in the sex shop, or you didn't ask for a blacklight from Janet (or you didn't use it).
I read through the walkthrough a couple of times and had the receipt Kyle dropped and both clues for the puddles in stall 2 and 3 before I consulted the walkthrough :/ maybe I should just restart the game? I did have to split it between two days cause I got stuck on one other part before figuring out the rest.
Hmm, I guess it's always possible that something's broken... So, if you have a save from before you started the investigation, you could see if that's the case.
Just to be clear, from the gloryholes you should have two puddles from stall #2 and one puddle from stall #3. And of course the business card. If you have all those, it should immediately move the story forward.