Im on. #3 and this baby definately moves a lot different (less) than my 1st 2. I also bought the sonoline b to listen to him whenever I worried.
Yes this is the same with me i felt my sons at 16 weeks and now im 24 weeks pregnant and i barley ever feel her move it worries me. Mu doctor says every pregnancy is different. I bought a Sonoline B baby heart beat monitor it works great and makea me feel better when i hear the heart beat. I dont know about extra flap though..
You should ask about where your placenta is placed. It may be taking the blows of the movements if it's on the front.
Good luck, that sounds scary but hopefully things fix themselves by him growing just a little more in there.