I brought Lucy to the ER Sunday morning and to her vet yesterday for a follow-up. The ER did a blood test which showed normal kidney function and no abnormalities there. They confirmed yesterday that her urinalysis shows abundant rod bacteria meaning a UTI, which is what was suspected due to her constant in and out of the litter box and peeing blood. The ER put her on amoxicillin the night I brought her home, which we have been giving her since. The vet is waiting on the culture to come back and confirm this is the right antibiotic. All that being said, I noticed Lucy was leaning to one side last night while she was sitting down to eat. When we woke up this morning, she was limping badly, favoring one side. I called her vet as soon as they opened and they said it sounds like an arthritis flare-up (they did x-rays several months ago and confirmed she has severe arthritis in her knees and elbows). They gave me more buprenex, which I have been giving her the past few days to help with the UTI, as well as some onsior, which is an anti-inflammatory (this particular medication is new to me, but they said it will help). She is still eating a good amount. Lucy has never had a flare up like this to the point where she is limping, so am trying to figure out what the heck is going on as she has had quite a busy past few months at the ER/vet (pancreatitis episode about a month ago). The vet did put her on a new food after the pancreatitis incident due to suspected IBD (Royal Canin venison), so am not sure if all of this happening is just a coincidence with that, the vet said the food did not cause any of this. She has never had a UTI before either. Could the stress on her body from the UTI have caused the arthritis flare up? Also, she was completely fine leading up to early Sunday morning when I woke up to her using the bathroom around the house and then brought her to the ER. Can a UTI happen that fast? The mention of 'abundant' bacteria has me concerned/confused, as she showed no signs leading up to that. I am just so worried with Christmas coming up, her vet being closed for 6 days, having no idea what is going on with her, and seeing her in pain... Edit: we live in a townhome with a very small set of stairs (there are 5 of them), but Lucy has food, water, and a cat box on both levels. We built her a ramp to use on the stairs but she does not use it.