What Causes Reddish Purple Vaginal Discharge?

Went to the doctor. He said I have a bacteria infection. I just got the metronidazol yesterday I haven't used it yet. Two days ago I used my old medication I got May of 2014. I did not use any yesterday or the day before. So today I use the rest room wipe and there is a clot of white discharge and red and purple discharge? Could it be from the bacteria? I also have polycystic ovaries