I've seen many pregnant women ask this question and I believe it's pretty common.
My son was the same way and I think what he was doing was pushing his feet off and almost "jumping". I
f it's quite frantic and you are very worried and don't have a good feeling about it, by all means visit an ER or someone to get your baby checked out. You never know and a mother's intuition is usually pretty good!
Hiya, could it be hiccups?? Hiccups are REALLY common and my baby got them at least twice a day from about 20-something weeks. Just a thought :-)
I would mention it to your midwife/doctor on your next antenatal visit or if its really bothering you make an app with your gp and talk to them about your concerns