Hi, My Wife Periods Comes On Around 14th Of Every

Hi, my wife periods comes on around 14th of every month. This time we had unprotected sex on 11th morning thinking that day before periods are safer days.
We were expecting normal periods on 14-15 but it didn't come. Then we decided to take Ipill. We had Ipill on 15th approx 86hrs after sex.
Next day of taking pill little dark blood came for very little time followed by very negligible liquid /blood flow.
Is she pregnant, is this implantation bleeding or bleeding as result of pill. We are really worried. We don't want to have a baby at this time.