In a normal menstrual cycle, hormones are produced by the brain which stimulate the ovaries to get an egg ready for ovulation and to produce estrogen. That estrogen production thickens the lining of the uterus, getting it ready for a pregnancy. After ovulation, the ovaries then produce progesterone, which stabilizes the uterine lining. When an ovulation does not result in a pregnancy, both hormone levels fall, which triggers the shedding of the uterine lining, causing a period.
Birth control pills contain estrogen and progesterone in every pill. Taken together, these hormones suppress brain stimulation of the ovaries so that you do not ovulate. In addition, estrogen and progesterone produce a stable and very thin uterine lining. In the placebo week of the birth control pills, there are no hormones in the pills and this lining will shed, resulting in a period. Some women taking birth control pills get such a thin uterine lining that there is nothing to shed, leading to skipped periods.
One important aside is that if you miss taking pills, you are at risk of ovulating. The highest time for this risk is forgetting to start a new pack of pills after taking all the placebo pills. If you forget to start a new pack, you are at risk of your brain triggering ovulation, which can lead to an accidental pregnancy.
Finally, let's talk about your question. Based on your description of the problem, I do not think that you are pregnant. But you should definitely take a pregnancy test. The morning after pill, although effective, is not 100 percent effective, but closer to 90 percent. Once you are sure that you are not pregnant, I would recommend you continue taking birth control pills as directed. Be pleased that you are one of the lucky gals who have the side of effect of no periods, or significantly reduced periods, when taking the pill.