So when did i actually get pregnant ??? My last period was dec. 21 through the 28th then i tested two weeks ago bfp

Tiffanie • I am 23 on baby #3 and hoping for a girl. I have two boys T is 4yrs and L is 2yrs. My EDD is 9-27-15
In lost on when I actually conceived I'm trying to use a prediction calendar and don't know what to put