Hi www, there's so much potential for worry, isn't there?
With my 1st, I felt him at 20 weeks, with my second (very close together) was fully expecting to feel him around 16 weeks but didn't, and got myself very worried about this. In the end didn't feel him till 20 weeks either. i'm now 18+4 and have only a couple of times felt this one, and like princesspeahead said, when I had my scan a couple of weeks ago & he/she was all over the place, and about 20 cm long, I thought it was wierd that I couldn't feel anything.
Of course, as others have said, you should check if you're worried.
One thing I do, although I can't feel the movements as such yet (apart from 1 or 2), if I lie flat on my back & put my hands on my belly, under belly button, I can sometimes feel wriggling vie my hands through my tummy, rather than internally, iykwim, and do this now most nights and usually feel a movement, once, a couple of weeks ago I even felt what must have been the leg - a long hard line from belly button down, and it was gone a couple of minutes later, maybe you could have some success with this & it will help you feel better?