Waiting for a kick

I'm 17 weeks 6 days and I still don't think I've felt any kicks. I think I felt SOMETHING? At 15 weeks but not totally sure if it was the baby or not it was just a light bubble feeling in my left hand side low down in my tummy I think it was. But why have I not felt anything since? It's starting to worry me a little now? Anyone not felt ther baby yet at this stage?