how soon can I take birth control after plan B

I took a plan B pill on February 24, I will be getting on birth control pills but I was wondering how soon can I get on them considering I took plan B? Can I just get on them right away? Will it affect the effectiveness of the birth control? Will my period come on week 4 of the birth control pack? because I have read that plan B can delay or make your period come early...

p.s i don’t want to start birth control on the first day of my period because I am irregular so i have no idea when it will come, so the sooner I get on birth control the better