My Nikon D5100 s autofocus doesn't work in a nightclub?

So I work as a nightclub photographer but my autofocus won't work meaning I have to take a dozen pictures every time using manual focus as i can't see if it is focused properly or not.

Is there a way of fixing this?

AF is always a problem in low light.
A fast prime lens would improve matters - 50mm f/1.4 for example.

A few things:
Get a camera with better AF in low-light situations.
Get a faster lens such as a 35mm f/1.4. The larger aperture will allow more light into the camera making it easier for the camera to focus.

OR, spend zero $$$ and just use hyper-focal focusing. Say you're in an environment where you know that your subjects are always going to be 4-8' away from you. Set your lens to a specific focal length, and choose an f/stop which will produce enough depth of field so that everything from 4' to 8' will be in focus. Then just tape the lens's focusing ring down so it doesn't move, put the camera to MF, and just snap away.

Do a youtube search on how to use hyper-focal focusing. If you use a prime lens, then it's easy because of the depth of field scale printed on the lens barrel. However, using a zoom, which doesn't have a dof scale, will require either an app, a cheat sheet on paper, or just good 'ol experience.

Turn on the auto-focus assist lamp.

Look on page 158 of your user manual.

In low light NO auto-focus will work.

If you have one of the Nikon external flash units, the auto-focus assist is accomplished by an IR lamp in the flash itself.

NOTE: If you are manually focusing your shots, the electronic rangefinder in the cameras viewfinder will tell you when you are in focus

Of course it doesn't. In the dark, focus manually.

It doesn't work because there isn't enough light. The camera can only do so much.