With my first child I did not feel any movement until about week 22. During my second pregnancy, I felt them around week 21. It might just be a little early.
Have you felt the baby move before but now you do not feel anything? Are you doing kick counts (you probably already know this, so sorry if I'm stating the obvious)? Sit or lie quietly and count the kicks within a 60-minute time period. You should get at least 12. Sometimes the baby may be asleep, so you may wish to check again.
Finally, if you need some peace of mind give your OB's office a call. They are there to help you and they get this sort of question all the time. Best wishes!