It is possible you have an anterior placenta. It makes it harder to feel baby move. Also, some women don't feel baby move until well after 20 weeks.
Some woman never feel the baby move. I felt my daughter early and all the time and by the end I had to keep my hands on my belly and count movements because I couldn't feel her from the inside anymore. My doctor told me she might have been on a nerve or something. Try drinking orange juice and laying on your left side. Good luck
It depends on a lot of things. Skinnier girls tend to feel it earlier on. Also people that have been previously pregnant feel movement earlier. I would worry about it yet. If you haven't had your 20 week ultrasound I'd ask about it then.