Confused??

Well three days ago I got a little spit of blood in my underwear so I decided to start taking birth control that day because I thought it was the first day of my period. However, now my “period” looks like it’s just spotting?? Did I take it at the right time and it stopped my period or was I just bleeding for a different reason?? I’m a new birth control user and I’m a healthy 18 year old girl! Please, I’m so confused!