The main ingredient in Plan B is a hormone. Therefore, you will experience nausea, period-like cramps, bleeding even. If you took it twice in a month, even more it will affect your period. This is a normal side effect of the medication. Honestly, Plan B is NOT a contraceptive method. It is an EMERGENCY contraceptive... not meant for you to use every time you have sex. Please consult with your OB/GYN so that together you can determine what the best method of birth control is for you.