16 weeks and not really feeling movement...

Aimee
With my first two pregnancies, I felt them move at around 14 weeks. And it was CONSTANT. Now, with number 3, I haven't felt anything really. I did read somewhere that this can happen with multiples, where you don't feel movement until 18-20 weeks. So I'm a little freaked out now. Should I be worried, or am I just stressing for nothing?