Heavy Bleeding after Period Ended

Hi, I was on Nurigynon birth control injection for the past 7 months. I stopped and took the last injection in November 6. Then missed the December injection and onwards. I had normal periods (light and 7 days like on the bc). The last period ended on Jan 2. Then on Jan 7 I got light pink discharge. Then it got heavier and heavier. And the past few days it was really heavy, with lots of clotting. At one point I felt light cramps.

It has sort of subdued. But I did have unprotected sex in December and January. I haven't taken a test yet. But could that be implantation or is this normal for coming off the bc?