Hi, I Took Postinor 2 On 10th December 2016 Which

Hi, I took postinor 2 on 10th December 2016 which was two days before my ovulation, after having unprotected sex. I took the first pill within 4 - 6 hrs after sex and the second pill 17 hours later because i forgot. My period was supposed to come on the 26th Dec but I am instead having tender nipples and fàint cramps. I did home pregnancy test and it came out negative. is it the postinor causing delay in my period or I'm pregnant?