help please

On halloween I lost my virginity, we used protection and I am on birth control. But I knew I was supposed to be on my period on halloween and I didn’t want to be so I started a new pack therefor I wouldn’t get my period. Ever since I have been bleeding but only the tiniest about of blood. Any one know why? Some people tell me it is just bc I switched the weeks and it is my body adjusting. If you have any advice please let me know, thank you!