Ahhh don't worry, yan pa lang talaga sa 18 weeks! A few of us moms didn't feel movement until around 20-22 weeks pa, especially if first time mom ka or if your placenta is in front (anterior placenta). You might start noticing those little flutters soon, some say it feels like butterflies or gas lang talaga haha, kaya madaling makaligtaan. If you're getting anxious though, no harm in checking with your OB para may peace of mind ka, and they can do a doppler to confirm baby's doing great!