Hello and welcome to EmpowHer,
First of all, you cannot become pregnant from outercourse even if there is pre-ejaculate. He must penetration you and ejaculate in order for pregnancy to occur. You took EC and you've had 3 periods since them. All these factors ensure that you are not pregnant.
Sometimes taking EC can cause hormonal changes that last over the course of a few months. Your hormones could still be off balances from that. However, if your symptoms continue, I suggest you see a gynecologist.