Hello dear Understand your concern As you are already on birth control pill generess fe, there is no need to take plan B pill (If you are taking it regularly). It is very effective in prevemting pegnancy, as failure rate is only 0.5-1 percent. But you used plab B pill already and it cause hormonal imbalance as it contain high progesterone. So along with generess fe it cause high progesterone level in the body and this is the reason for the nausea. Progesterone relax the smooth muscle of gastrointestinal tract and produce nausea. So do not worry, it will disappear in 3-5 days as progesterone level come back to normal. Take small frequent meal, avoid large mead and spicy and oily food. And take domperidone or ondansterone tablet. Hope this may help you Best regards Dr. Sagar