Dark picture taking on stage

You need to run it with aperture priority, and have the aperture as wide open as possible (The lower the number the better). You've got the kit lens, which is a notoriously poor performer in low light conditions, you should consider getting one of the Sigma DG lenses.

The other alternative is to get as close up to the stage as possible, and use the smaller lens that would have come with the camera kit. It's a little faster.