Plan b or no?

Allyson

So just the other day (sunday), i had gotten on birth control but only took one pill since I got the IUD monday, thing is my boyfriend had came inside me on both those days, and now im not sure as to if we should get plan b, i ovulate in 3 days or so the app says, and my period lasted from the 27th to the end of jan, should i get a plan b still?