Hi, I Am 20 Years Old And Sexually Active. I

Hi, I am 20 years old and sexually active. I just started to take vitamins about two and a half weeks ago because my boyfriend said it's a good routine. My period is never late and I'm now three days late. I started to take iron, B12, vitamin C, and magnesium. I don't believe I am pregnant I don't know if it's too early to tell or if me not getting my period is due to me starting all these pills at once in the middle of my cycle.