Can you clarify some? Are we talking about urgency?

Or high volume of dilute urine?

The urge to urinate may indicate a bladder infection. If you are an older male the urge may be prostatitis, or bladder infection.

The volume of urine output, indicates high volume of water being consumed, or diuretics like caffeine in tea/coffee etc. High volume coming out without high volume going in, would be dehydrating.

I'd add the supplements back one by one...to see where the culprit is. Start with the B12... It's dose is so tiny it should not have much effect on the kidney. My guess would be the magnesium (depending on the dose)

I have seen people remark about taking high dose Bcomplex creating more urination. Often this happens within 2 hrs of taking 50mg or more.

What prescription did he give you? What type of cancer did you have?

Can you post here the doses you were taking of the supplements?
Also does your CoQ-10 have bioperine in it? This is a pepper extract, and some people cannot tolerate the pepper part.