How quickly does birth control work?

Mary • Hi! I`m Mary. I have a BA in Psychology. Been dealing with PCOS for 22 years. I work at Sander’s Candy and Ice Cream Shop and trying to get my head around this COVID craziness!
Hi all, 
​I'm officially a "secular" woman now and have started on the pill. (Giggles!) I noticed that even on day 1 of the pill that my period was very light, not that I'm complaining, but should I be worried? Does the pill work that quickly typically or do I have something to worry about?