Greetings.
So severe problem of difficulty even with a walker is quite uncommon with a bladder infection, though any severe infection of any organ in body may cause muscle weakness. Whenever there is a muscle weakness of this sort, following investigations should be done (if not already done);
1) Muscle enzymes; these are blood tests like CPK.
2) Electromyography (EMG)
3) Ultrasound of the abdomen and pelvis
4) MRI of the lower back
Please feel free for your follow up questions.
Dr. Arun
Doctor (MD)
MBBS, MS (General Surgery), Post-doctoral Fellowship in Sports Medicine