Period lasting more than 12 days?!

Natali • snap me at narellano707

So I've been on my period for 12 whole days now, and I'm really starting to get worried. Usually, I never last longer than 8 days. But here I am, on the 12th day of my period and the flow hasn't even lightened or darkened like it usually does. Should I see a doctor or just wait it out? Btw, I'm 17 years old and sexually active (Usually use condoms)