What Could Cause Early Periods?

Good day. I just want to consult about my period. I am taking birth control pill for almost 2 years now. And I decided to stop when i finish the tablets in the pack last 14th of July. But my husband and I don t want to have a baby yet. We were planning to use condoms instead. I had my last period from 9th to 13th of July. But our last sex was on 5th of July with condom as well. Unfortunately, today, 19th of July I had my period again. What might be the cause of this? Am i pregnant? Or is there any other reason behind?