Menstruating too long!

Katie • 21, 4"10. Happy
My period is usually at least 5-7 days long with just two days of spotting in the end, but this time is different. I still am having a heavy flow and its day 10. This has never happened before. The only thing different is my boyfriend and I had sex because I thought it was over. Could that have anything to do with this extended period?And I'm getting worried. 
Any suggestion or possibilities of what this could be? 
Please help!