Advice..?

Okay so. 
I thought I was pregnant then I fell really hard on my ass and knocked the wind out of myself. And I got my period on my estimated start day but I've been bleeding for 8 days now and I normally only bleed 4-6 days. 
Does anyone have any guesses what it could be that's wrong? 
What should I do? 
Wait to see if it stops or see a doctor immediately?
And I have been having sex for 4 years now. And this has never happened. 

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