Crepe Myrtle Won't Bloom?

I planted a crepe myrtle tree about 3 years ago. It has grown in size and is probably about 9 feet tall now. However, it has never bloomed. It had flowers when we first got the tree, but after that they never came back. Do I need to prune the tree in order for it to bloom? I get sad every year when it doesn't bloom.

By Katie W.