abnormal bleeding?

I’ve been on the pill for about a year now and i switched brands about 6 months ago, but im pretty sure it’s the same level of hormones. Usually i get my period halfway thru the week of my sugar pills, but last month I got it a whole week early before I even finished the hormone pills. I just thought that was weird because I thought my body would be accustomed to the hormones by this point and I take my pills on time. I was just wondering if anyone experienced this and if there was any other underlying reason for the bleeding.