You could have just a yeast infection or a bacterial infection. If one of you was not faithful, it could be an std, but it is probably a bacterial infection. If you go to your doctor or a clinic they just take a "sample" and look at it under a microscope to see what kind of bacteria is causing your discharge. If it is bacterial they will give you an antibiotic and if it is a yeast infection they will either give you a cream insert or a pill. They will tell you then if they recommend another std test or not.