Electric shock feeling 'down below'?

I'm 38 weeks pregnant and over the last week I've been experiencing electric shock type feelings 'down below', like a train going through a tunnel, just powered by a taser? What is it? :/ I'm not sure whether it's baby moving putting pressure on a nerve or my cervix changing, or what? Any experience with this at all? I've been getting it a lot lately and it's rather uncomfortable, it makes me jump! It happens when buba is staying still too, so not sure if it could be just down to him moving on a nerve?