not a yeast infection and negative on all stds?

can anyone help? i am 22 years of age and ive gotten tested atleast 4 times this summer..my ex bf gave me chlymidia but i got it treated...its been atleast 3-4 months now and i have this very bad fishy odor on and off also a white thick discharge and sometimes yellow..i recently got tested again and the doctor told me to use prephresh but it didnt work..im sure its not a yeast infection and im negative on all stds...i dont know what else to do..can someone help?