Super long period

So my period is now 14 days long this cycle and it's usually 5-7 days. I keep telling my mom that I need to see a doctor, but even though she hasn't said no, she hasn't really done anything about finding me a doctor (I'm 16 and we just moved to a new state). It's not heavy but it's defiantly not spotting. I've had a period for years and I'm pretty familiar with how my vagina works so I know something is up. 
Basically I'm just asking the older women out there with a bit more experience: how worried should I be? (I know someone is going to think STD even though I'm 80% positive that's not a symptom- just to clear the air, I'm a virgin)