It sounds like you might have a touch of SPD, or possibly your cervix is starting to dilate a little in preparation for labour. In case it is SPD try and keep your knees together when getting up/into a car/our of bed, etc, and this should stop it getting any worse. If your cervix is starting to dilate then don't get too excited, labour could still be weeks away it is just your body getting ready.

T
xx

ETA of course if you are worried then go and see your midwife