Why has my urine turned bright yellow?
Riboflavin. It is entirely normal, and it happens with any B complex too.
Is riboflavin the same as B2?
Yes, two names for the same vitamin.
Should I take B2 on its own?
A complex is the sensible default. Single high-strength B2 is generally taken for a particular reason.
Can I take too much?
It is water soluble and the excess is passed, which makes it difficult to overdo. Still check for overlap with a multivitamin.