Well, yes, pregnancy is always a possibility, but, you know, you can say that for everything in life... that really doesn't solve anything. The thing is - hormones from birth control pill stop your ovulation (release of the fertile egg) each month, if you take them relatively on time and the longer you take them the bigger the chances that your ovulation has stopped and that it will take time for your menstrual cycle (without BC) to return to normal. Because ovulation is what triggers the hormones to supply the tissue of your uterus with blood so that they can accept potentially fertile egg and the menstrual bleeding happens because this this tissue sheds to make the place for the next cycle. But that is not what is happening when you are on birth control - on the pill, you bleed because when you take sugar pills, lack of hormones your body is used to by you taking the active pills, causes the bleeding. So, the longer you are on the pill (or any kind of hormonal birth control) the bigger are chances your period will become lighter or even stop. How long have you been on the pill and which one?