Late period?

So I got nexplanon out in the beginning of October because it was messing with my period really bad. I'd bleed heavily for 3 weeks straight, then off a week, then start again for another 3 weeks. Now I'm 5 days late, but two weeks ago I spotted a tiny little bit for two days only. It wasn't enough to be considered a real period in my opinion. I have had unprotected sex a few times, but the pregnancy test says negative. Am I pregnant and testing too early, or is my body adjusting from being off BC?