STD and Metronidazole

I was dignose with an S.T.D im not sure what it was called but the doctor put me on 250mg of APO METRONIDAZOLE. He said that it would begin working right away. When he said that I asssumed that ment that the pain in my vigina would go away and the medicine would begin fighting the infection. I have been taking now for 3 days with instruitions to take 2 pills 3 times a day, also to take a bath 3 times a day. Since doing this i have not had as much discharge. I still getting a burning sensation with i place myself in certin posisions and when i use the bathroom. Today it is day three of the medication and i am bleeding lightly alone with some discharge.
I want to know if the pills are doing the job and fighting away this infection