My period is 3 days late!

So my period is 3 days late and I’m confused. I had sex with my mate and we used a condom. I also took a Plan B just to be on the safe side since I’m transitioning to a new birth control. My period has been really weird this year. I was 7 days early last month and 3 days early the month before. I took a pregnancy test on Wednesday, but it came back negative. My cycle is all out of whack. I was thinking about taking an ovulation test to see where I am in my cycle. Any advice?