I don't believe in God. What now? I feel empty.....?

You are just going through the normal grieving process that comes along with losing your faith. It's to be expected. Hang in there, and you will find yourself more and more fulfilled as you discover that you can live life on your terms, and enjoy every second of it, since you are no longer subject to the rules of some deity. However, I can't tell you why we're here. Take some philosophy cles. They won't give you the answer either, but they will lend some new perspective.