What should I do?

Hey guys! So I was on birth control and ended a month or so ago (from the time I started up til now my boyfriend has came in me on occasion). Well once I ended I assumed I’d start bleeding excessively but that actually didn’t happen. I got my regular period in the beginning of December and was fine.

My next period was supposed to come December 31st and has yet to come. I haven’t been really feeling like myself lately and everyone around me has definitely started to notice. My boyfriend and I took a test last night but it came back negative.

Could it be late side effects of me stopping the birth control?