I have never had it take more than the end of the next day on United.

Have you checked the status on their online system?

https://www.ua2go.com/bag/baggageClaim.do

What does it say there?

It's pretty baffling how they are just randomly sending you bags, it's possible they gave your bag to somebody else (left it at their front door, a hotel front desk or something) and it's just sitting there now.

I would be starting to worry if I were you, you may not be seeing your bag anytime soon. If they don't know where it is, it's probably gone, if it's at the airport, it may make sense for you to go and try to get it instead of this silly delivering the totally wrong bag over and over again.