Hello ma am and welcome. You should have mentioned which birth control pill you are on exactly, as some of them can cause a withdrawal bleed almost instantaneously. But then again, this also depends on your personal systemic response, hormone levels, and various other factors. I do not think this is a cause for concern or that there is any abnormality of sorts; but I would although like to pay emphasis to your age which could be an added factor. You are at an age wherein you will be soon approaching menopause, and so hormonal fluctuations are normal and you may require some advise or attention from your doctor although this is nothing urgent and can wait until your next appointment. Best wishes.