Worried.

Does growth slow down at 18 weeks? I haven't felt any actual kicks yet and my nausea went away a couple weeks ago. But I can usually feel flutters from my twins and the last couple days I haven't. Are they slowing down or should I be worried? I have an appointment Wednesday so I can find everything out then. I'm just kind of dreaming out. I had a miscarriage a little over a year ago and it was no heart beat at 8 weeks.