Am I pregnant?

I have been on bc pills for the past 10 years and recently stopped taking them in August. I have had a period every month since August but every month my period keeps happening later and later than the previous months. It’s December now and I should have started my period around the 4th (if I was going off of my last period in November) but I haven’t started yet and it’s now the 12th. I took 2 home pregnancy test but they are both negative. Could this be because my body is not used to being off the pill? I don’t remember if I had irregular periods because I got on the pill when I was 16 and am now 27.