When i started getting into bb-ing when i was 15 i decided i was going to get huge by taking like 5 daily multivitamins a day and my urine was SO neon yellow i swear if you shut the lights off it glowed in the dark.
Whatever you are taking you are taking more than you are absorbing and excreting the rest. Option 1) cut back on the supps a bit or Option 2) drink your own urine to absorb what you missed during the first pass.
As far as whether or not it is the vitamin b, very possible. Can you list what you take on a daily basis with dosing so we can possibly suggest where you can cut the dose (saving both $$ and maximizing efficiency).