15 Months & Waking Up 3 Times A Night?

What is wrong with my child? I cannot answer this, but if someone could I would really appreicate it. It was a horrible night last night, it really was and honestly I do not know why. But alls I can tell you is that Jeff woke up at 12:00, 1:20, and 3:30! The child is exhausted and needs to sleep, but he just doesn't want too. I'm at my whits end and not sure what to do anymore...