This is my first baby, and I too had an anterior placenta and didnt feel anything until 21ish weeks, and even then it was only 2 kicks (tiny soft ones) a day for the first 2 or 3 weeks, gradually getting more and stronger...
Have you tried the lying on your left side and drinking iced water? See if you can feel anything then?
If you are really worried, call your MW and pop in and get her to listen to hte HB with the doppler... Im sure its fine though