It could be the catheter as I've had 2 due to post birth complications and my urethra was a tad stretched. I think it could have happened anyway as a lot of the stretching when you give birth is at the top of your vulva. I felt as much burning there as the perineum definitely.
I guess having had the epidural you didn't feel that sensation. I know I wasn't expecting it up the top area. So much of my antenatal classes focussed on the perineum so when I was birthing Mason I kind of freaked out a bit.

I'm sure it will shrink back soon though. You are still in the healing stage post birth. I think mine has but I haven't looked for a while