Female Hamsters Butt is Swollen

Question
Hello, I noticed today that my female Syrian Hamster's butt is getting bigger.

She was 7 weeks when i got her, and I've only had her a few months, so she's maybe 4 months old. So i thought maybe she was just getting "bigger" in her bottom half. But it's just so much bigger and its a pinky red.

It doesn't stick out past her tail, but it's swollen out and down towards the ground if that makes sense. And there seems to be a more red swollen bump where i think her Bum hole is. About the size of a dime.

Her tail doesn't feel wet, and she doesn't have diahrea, but her pop today was a bit softer looking.

Also last week she was sleeping in a closed in house and found out she was peeing AND sleeping in there when i cleaned her cage. So i didn't put the lid back on. Could her sleeping in her own Pee have caused it?

Please any help would be appreciated, this is my first hamster since i was a child... so I'm worried
Thanks so much

PS... She hasn't been near another hamster in 3 months, so she's not Pregnant :)

Also she still seems to be eating fine and drinking water, I have mostly only fed her the "hamster food" that is their staple diet, with the odd treat maybe twice a week. I haven't feed to much fruits/veggies as i was scared of her getting diahrea.

She walks fine and runs "Ok"... she used to be a speed demon, but she seems to waddle her back legs, I'm assuming to her enlarged butt, when she runs

Sorry i know this is LONG i was trying to be as detailed as possible to help you with your answer hehe
THANKS AGAIN

Answer
I am not a hamster expert by any means but I got a question just the other day from someone with a four month old hamster and she had just been diagnosed with an abdominal tumor.

You really need to get her to the vet's and get a definitive diagnosis.
That is the only way you will know for sure what it is.