After birth mom cat has lump

Hi my cat had her kittens 2 days ago and since we have felt a firm lump on her right side near her hip. I have a call into the vet. I was wondering if anyone knows what this may be. I found a thread from 2 years ago that described it but there was no conclusion posted. The following was posted to that thread:
She is acting normal, eating using the litter box and caring for her 5 kittens.
Thank you

Follow up: The vet examined her. She is having incontinence issues from the birth. It was her very full bladder we were feeling.

Hi and welcome! I'm glad to hear her problem has been solved. I've never heard of such a thing before. We learn something new every day! She's a pretty kitty.

Thank you.

Very sweet kittens! So glad mom's issue is resolved too! [emoji]128522[/emoji]