Not getting periods. Any other reason?

Hello, I am not getting periods since the last period and now 34 days already pass. I had sex on December 23rd and no ejaculation inside the vagina as he remove before he came. And I took ipill after 14 hours of our sex. The next 3rd day I bleed for 4 days that means on 28 decmbr after 28 December I got a normal period upto 3rd of jan 2017. Then I got periods again on 29 of January. Then I thought that I would get on my normal date which is 13 or 14 but I got on 24 of Feb 2017, So this month i.e March my normal date (12-14) passed and also 24 passed whic i got last time. When I count the days It's already 34 days gone. What is the reason for the delay? I don't think it will be a pregnancy as I took ipill already and got 3 times periods and did pregnancy test 2 times with negative results. Is it due to ipil? Or is there any other reason?