Pinching feeling inside vagina when baby moves

Ok ladies, im almost 38 weeks. It feels like really hard pinching on the inside of my vagina sometimes and it's really uncomfortable and sore. It feels quite low down, and it's not really lightening crotch pain as I've had that too but this is different. It's usually when I'm sitting back relaxing or lying down and i can feel baby moving at the same time. Baby is head down but not yet engaged. Is anyone else experiencing this? Or have any explanation?