Stitch pain in side 27w6d

Twice in the last 12 hours I have been laid on my side (one time on each side) and have all of a sudden had a stabbing pain in my side, like really bad stitch. It absolutely kills to move, but once I have sat up it does ease off, though there is residual pain in that area for like a half hour afterwards :-/

I've not phoned my midwife yet as the pain eased off straight away once I moved and not getting any other symptoms.

Just wondering has anybody else had this? Does anyone know what it could be???