HI Keys the answer is that a cancer DX has never helped anyone's sex drive that I know of. I know for myself it was not on my top priority list until things evened out. For a while it is as if there is not enough room in your mind for anything else except dealing, Stress, fear, helplessness, anger, hopelessness and on and on the emotional you deal with for a while are almost endless. Then there are the physical urgency, burning and again on and on. I have not heard of BCG being linked to lack of sexual desire but that would be better asked to someone who has a PH.D. at the end of thier name. Systemic chemotherapy can have an affect of hormone production though. Once you get through the barrage hopefully things will get better. If you have had a good physical and your doctors rule out any physical reason here are a few things that might help. I have found that talking to a therapist was a great help in dealing with my emotions and fears and putting things in perspective. Also maybe meditation, yoga or walking to reduce stress. I hope this is some help.
P. S. A date night might not be a bad idea either it takes time to get back to the place you were before this shock as a couple.