anterior placenta

I went for an ultrasound about a week ago and I told them I was almost 20 weeks and didn't feel a thing! Well the US tech told me I have an anterior placenta this is the first baby I've had this with and my 4th pregnancy it's so sad because this is the last one and I'm half way into my pregnancy and I feel nothing... my question is IF you have had an anterior placenta around how many weeks did you feel your baby move I'm almost 21 weeks now and still nothing :(