I understand that sometimes it depends on the location of your placenta as it might be in the way for you to hear your baby. But since baby seems to be growing dont be too anxious. Maybe when you go for your ultrasound ask the technician the location of placenta and the baby position and explain that you cant feel baby movements.
You're still early, especially If it's your first, with my kids it was more around 25 or more weeks I felt kicks its more like butterfly flutters until your further along. Don't worry