None of us know why your gf had a 12 day period, only a doctor would know that. But if she did in fact, have a period, and got a negative test, shes probably not pregnant.
Is she as freaked out as you are?
If your scared to make a doctor app. Or dont know how, look up the closest doctor to you, and I will call and make an app for you, and alls youll have to do is go.
People are trying to help you, but you have to want to listen.