Late Period from Going off the Pill?

Lauryn
hey! 
i went off the hormonal birth control pill in december. i've had a period every month since then, but i have not had this month's yet. it was supposed to start february 1st, but as you can see: it is now the 13th--and still no period! 
i had protected sex 3 days into my period being late and he didn't finish, so i don't really think i'm pregnant. i also don't have any symptoms (although my left boob is sometimes slightly sore, but that's normal). 
i took antibiotics before my period was supposed to come. i was taking amoxicillin 3 times a day for 1 week. 
is it normal to have a late period after going off the pill? will my period come? i'm not even experiencing any period symptoms (i usually don't, anyways, but i can feel it coming). 
or could it be the antibiotics? or both?