Does birth control still work if my period's aren't synced up to it?

I have been on Gianvi in the past. Have you talked with your On/Gyn about this? I am on Beyaz right now (basically the same thing as Yaz, which Gianvi is generic for) and Beyaz also has only 4 placebo pills too. Sometimes my period also comes late and continues into the first week of active pills in my new pack. Gianvi, Yaz & Beyaz have always been effective for me as contraceptives, and I have been on both Yaz & Gianvi for quite some time each in the past also.
Did your last bc pill contain a different amount of placebo pills (most common = 7 days)? If so, your body is most still likely trying to adjust. If I skip the placebo pills one month (I have my Ob/Gyn's okay to do this) and thus start my new pack early, it can also skew my periods and they have also come alter the next month I don't skip the placebo pills! As long as you are taking the Gianvi every single day (preferably at the same time each day), you shouldn't have a problem with its effectiveness (unless you are overweight as it is considered a low dose bc pill & in that case pls call your gynecologist immediately).