What can cause yellow discharge and odor, negative on std test, and just got treated on yeast infection?

Bacterial vaginosis: Bacterial vaginosis (BV) is the most common cause for a yellow vaginal discharge with odor. BV is not an STD.

Vaginitis: You probably have a bacterial vaginal infection. This would not respond to treatment for yeast and would be negative on STD test. See your doctor, antibiotic would help this.

Bacterial Vaginosis: Any change in the normal flora in the vagina can affect the smell, colour, or texture of the discharge. However with a negative STD results it is probably more than likely Bacterial Vaginosis. Bacterial Vaginosis is a bacterial infection that is not sexually transmitted.