Help!

So I recently lost my virginity not too long ago, and have only had one period (a very short period) since then. I took one pregnancy test almost a week ago, and it came out negative. But I will probably take another one just in case! Does anyone know what this may be? I have heard that sex can throw your cycle off a bit, but do not know if that is the case or not. Please let me know if you have any info that could help me, thank you!