a strange sensation in my belly :{ NORMAL????

gstore

k, so this might be completely normal, but i just have to ask.... today and yesterday i've had 2 or 3 weird feelings in my lower belly where baby girl is.  i'm 21 weeks tomorrow.  the feeling is like...a surge of energy.  like some sort of fluctuation, movement or...heaviness.  i know what it feels like for her hands and feet to move, so it's not that.  the sensation makes me want to stop and hold my belly and wait it out, and it lasts about 5 seconds or so.  feels like she just grew a pound in an instant and i have to hold her up.  not nausea.  not dizzy.  not sharp.  just heavy and sorta whirly.  weird?  normal?  i'll run it by my midwife next appt, but i thought i'd ask you in the meantime.  would appreciate any help you may have.  thanks!