The same happened me Im 19 weeks and 1 day by my dates 18 weeks and 4 days by scan but last week i was feeling regular little kicks low down on my left side then nothing for nearly a week then the last two days im feeling movement it did worry me even though this is my 4th baby and i remember the others doing the same but i was thinking of seeing if i could get a scan but thankfully baby is moving nicely again