I’ve been on alesse-28 birth control since November I believe since the end of November, my period

... has been coming on time during the white inactive pills- even though it slightly different. However this month I got my period 3 days prior to the white pills- is this normal. I did lose a pill by it falling out of my pack, I just continued like normal and haven’t missed any- but I will be one pink pill short this month. So I’m not sure why it’s so early if I haven’t done anything wrong by missing a pill or taking it late