Sounds like bacterial vaginosis (BV). Not an STD in itself, but its presence can increase your risk of contracting an STD from an infected partner. Trichomonas (an STD) can also cause this symptom. You will need to see a physician who can look at the vaginal secretions under the microscope, to determine if its the BV ot Trichomonas.
check out vaginosis. you may have bacterial type. here is a link you can use to start your search. http://womenshealth.about.com/cs/vaginosis/a/bacterialvagin.htm