With my daughter I felt movement at 17 weeks, and it felt like something was tickling me from the inside. Almost like if you run your fingers down your arm, and it tickles and itches? Basically like that. It wasn't until 19-20 weeks I started to feel kicking.
With my first pregnancy I think I was around 21 weeks or so. With my current pregnancy (2nd) It was around 17-18 weeks. It feels like butterflies. I don't know how else to explain it. Sometimes if I'm not really paying attention and she's wiggling up high it feels like gas though. I can usually only feel her at night when I'm really still and trying to pay attention to her moving.