That's normal. It depends on your body structure and the baby's position. You should start to feel movement before week 25 :)
Tomorrow I'll be 20wks, and I don't have any movement yet :-( hopefully soon though, I can't wait...this is my first pregnancy.
With my 1st I didn't feel movement until 21weeks. It should be real soon!! It's a wonderful feeling, I miss it. :)
Have you felt any little tickles at all? With baby #1 & #2 I felt fluttering and tickle like sensations at 12weeks. Then kicks or thumps at 23weeks with both pregnancies. You should feel something by now