Any advice?

So I’m on this three month birth control so I only have my period every three months. I’m on the second month of pills and I’ve started having this kind of early bleeding like in the very beginning of your period and idk why. I’ve been on this birth control before and only had this issue when I hadn’t been consistent with it but I have been. My sister just moved back home and just started her period so maybe that’s a part of it? Should I be concerned?