Advice??

Im currently breastfeeding and had my iud removed on 9/10, we had unprotected sex on 9/14. We bought ovulation tests and i took one the next day and it said low fertility, i tested two days later and it went to high fertility, so i took a plan b that exact day it said high fertility, because the night before we also had unprotected sex. I tested yesterday it still said high fertility ( the flashing smiley face on a clear blue fertility test). And i also took a pregnancy test, it was negative. However this morning i woke up spotting brown, cramping & bloating. I have no idea when my last cycle was, because with my iud i bled constantly.

Is this more then likely from the plan b? Or implantation bleeding.