Weird pain in my left side

[Sunseal]

Hi ladies
This morning I have woken up with a weird pain in the left side of my belly, quite far out towards my side. It feels quite achey and I thought that it was muscular as it gets worse when I move/when I can feel the muscle there working. This made me think RL pain.
But, when I'm just laying flat, it seems to throb with my pulse?
Any ideas what this could be? Just listened to baby on the doppler and heartbeat is fine and she's moving around a goodun in there.

 

[JT2013]

Don't know what this is but it sounds very similar to what I have been having the past few days. Really uncomfortable...I am making the assumption that it's just stretching etc and the baby does seem to be lying on that side at the moment so that might also have something to do with it for me!