I would definitely suggest that your joint pain examined.
Though it is rare but systemic side effects happen even most side effects are local to bladder.
They call the symptom "reactive arthritis". There are several papers published but mainly dealing with
a single patient case with arthritis like symptoms. Interesting, those papers are published mostly by rheumatology department. There is a paper published in Italy in 2013, which had summarized the various published papers.
73 males patients and 16 female patients who had developed arthritis like symptoms.
The symptoms of reactive arthritis appeared after average of 5.8 BCG instillation. It is similar to your situation.
Polyarthritis was present in 55.1% of the patients. 51% symmetric and 49% asymmetric
Oligoarthritis was present in 37.0% of the patients. 33% symmetric and 66.7% asymmetric
Monoarthritis was present in 7.9% of the patients.
Overall, an symmetric distribution of arthritis was 59.6%.
Knees and ankle were the joints most frequently involved.
The antigen HLA B27 was positive in 42.6%.
The synovial fluid analysis was defined as as flogistic-aseptic in 71.9% of the patients.
Arthritis was recovered within 6 months in 93.2% of the cases. That is a good new.
70.5% of the patients within the first two months.
NSAIDs, ( i.e. asprin, ibuprofen, Advil are over the counter NSAID drugs) and Corticosteroids ( also known as glucocorticoids) were administered alone in 65.1% of cases, and in conjunction with other drugs in 40.4% of the cases.
Other hospitals seem to arthritis like symptoms seriously. The report indicates over 90% of cases were recovered with proper treatment.
It is important that you seek medical advise soon for your arthritis symptoms, which is likely a side effect of BCG treatment. Once you recover, you may be able to restart BCG treatment.
Below is the link of the research paper. You may want to show it your doctor.
www.sciencedirect.com/science/article/abs/pii/S1568997213001213?via%3Dihub
Below are the definitions of some terms from Googling
Polyarthritis refers to a joint disease that involves at least five joints. One or more signs of inflammation, including pain, movement restriction, swelling, warmth, and redness, are seen in the joints involved.
Oligoarthritis (from Greek oligos - 'few') is defined as arthritis affecting two to four joints during the first six months of disease.
Monoarthritis is inflammation of one joint characterized by joint swelling, pain, warmth, and sometimes fever and periarticular erythema. Arthritis is often associated with joint stiffness and total loss or decreased range of motion.
HLA-B12 Antigen Test (Blood Test)
To determine whether you have human leukocyte antigen B27 (HLA-B27) on the surface of your cells; to help assess the likelihood that you have an autoimmune disorder associated with the presence of HLA-B27
A Synovial Fluid Analysis is a group of tests that checks for disorders that affect the joints. The tests usually include the following: An exam of physical qualities of the fluid, such as its color and thickness. Chemical tests to check for changes in the fluid's chemicals.
Best wishes