What Causes Fishy Smelly Discharge?

I have a fishy smelly discharge. I went to the doctor and she said it was nothing to worry about it happen in all women and you have to get some pills to fix it. It smell like fish all the time an she called it HVS how do i fix it and is it related to a STD if so how do i fix it. It a apeers to come when i am not well. I have had thrush recently and a urine infection is it related this smelly fishy discharge.