Bulging Vagina

Ok, really embarrassing post but here goes. My vagina has been sore for a week or so even though I haven't had sex recently. Figured it was nothing, then today while I was going #2 (or trying to, been super constipated) I felt my vagina bulging out. Almost like something was pressing from the inside. I know the baby is ok because I just had a sonogram today, but what the heck is up with my vagina? Has anyone experienced this??