Just returned from physio for the sciatica that I've had for the last 4 months. Therapist immediately said 'ooh you've got joint hypermobility' and discovered that I've been walking limping about with my seat bones out of line. She twisted me round in several different directions at once until we heard a nice loud clunk. It feels so much better.
She also said "absolutely no birthing ball exercises, no squatting, nothing at all to open up the pelvis - it's open enough already". Any sharp pain in the vaginal area is actually the gristly bit that joins the front of the pelvis giving way. And no yoga. All these will only make it worse.
And out of interest, those who do have joint hypermobility - did you have fast births?