I am 23 years old.I don't have any health problem,I'm using daily niacin500mg it's good for health?

You should study some books about nutrition so you know what effects to expect. You apparently know that niacin amide makes you itch, but it has some other nicer effects. There are between 13 and 17 B vitamins, depending on who does the counting. B2 is a water soluble dye that turns urine bright yellow. When the color fades it's time for another pill. These books are still the most popular introduction to the subject:
www.amazon.com/Adelle-Davis/e/B001J3RULO
www.adelledavis.org/
cronometer.com/ (I haven't tried the software.)