What Causes Brown Watery Vaginal Discharge?

Hi I have a brown watery discharge that started today. I ended my period about 4 days ago. I'm 16 and I'm not sexually active. I have researched a little bit and I don't think I have a yeast infection, but I'm not sure. This has never happened before and I'm not sure what it could be. I know it's not a lot of information, but i would love even the slightest help on what's going on. Thank you!