ahhh well...im slightly worried...

i had sex for the first time with my boyfriend...we were both virgins. anyway i started bleeding after it...it was light but then the day after got heavy and last for 7 days...im not quite sure...was that my period coming early...cause i was meant to get my period last week...and there is still no sign of it.
could it just be late or could i be pregnant?
we did use protection, but does being sexually active change your period cycle?
im quite confused and just wondering...
please help if you can