Cat randomly peed on bed

Hi guys 👋, so I have a female cat that I adopted in February, she’s been spayed and medically treated. She’s always used her litter and been so playful. Randomly yesterday she came out the room and has been walking weird as if her back legs hurt. I can see her body tensed and she peed on my bed this morning and she’s never did that before. We got a new kitten a few weeks ago and at first they didn’t like each other but now they’re very playful. I don’t know whats going on with her, should I be concerned and what could it be?