Welcome to the Forum!!
We are very fortunate to have BCG available. It is the current standard of treatment for bladder cancer in situ and for high grade bladder cancer that is still non-invasive. While it does have side effects, for most people they are relatively minor and quite tolerable....nothing like what patients who need to undergo traditional chemotherapy have. There is a LOT of information from others who have had BCG on this Forum. Just go to the very top of this page and type "BCG" into the Search area.
I will just give you my experience. I was diagnosed with CIS and had an induction series of six doses, once a week. Then I was on a maintenance series of once a week for three weeks every three months until two years had passed. I have now been bladder cancer-free for almost 14 years.
BCG side effects usually start out very mild and then increase as the body's immune system kicks in...which is what you WANT to happen. During the first few hours as you hold the BCG in your bladder and then pee it out there is discomfort, burning, and urgency. The next day it is common to feel fatigued. Sometimes the burning and urgency continue for a while. A the treatments continue these side effects do worsen. As they became more uncomfortable for me, my urologist reduced the dose to 1/3 of the original. But I made it through to the end.
Some patients do have more serious side effects and need to discontinue the treatments. There are other options than BCG, but they are not as effective.
As you read the comments about BCG on the Forum, please remember that people who have problems are much more likely to post than those who have none!
The odds are that you will be fine!