I barely felt the baby move, maybe once a day if I concentrated? I also had an anterior placenta. I had lots of scans due to small size, and everytime they asked me about movements I said 'no not much but that's normal for him' (and didn't think anymore of it). It wasn't until I read my notes that I saw that was one of the reasons I was induced (lack of movement, as well as other stuff). So just to say just keep being honest with your mw but also don't panic at all. Just be aware of what's normal for you. And congratulations!
Anterior placenta can really cushion baby's movements - I've only just started feeling anything (21 weeks, 2nd baby) and all the movement I do feel is much lower down than with the first. I had posterior placenta with DS and felt a lot more then, even at this stage.
I think it is normal to start feeling some movement around 20 weeks but that it is sporadic. See if you notice patterns when baby is more active (for me is around 10am, 2pm and 9pm) and what movement is normal for you. As baby grows you will feel them move a lot more too.
Can also try drinking cold or sugary drink and having a sit down. I was out last night and had a Coke and baby was dancing up a storm for a while after. If you are very worried then contact maternity unit - they can give more advice and give you an US if necessary.