Aiyo, period yang tak sama mcm biasa memang boleh buat paranoid kan! A few of my mum friends pun pernah experience period yang sikit je atau datang awal-awal, especially kalau stress, sleep deprived, or ada perubahan dalam routine makan ubat, sometimes even minor changes mcm timing makan pill boleh affect hormones kau. Since you're on the 21-day pill, timing shifting by a day or two is actually boleh jadi normal, tapi kalau flow-nya jauh berbeza dari usual dan you're worried, best to check with your doctor or gynae je to rule out anything, sebab they can see your pattern dan advise properly!