Vaginal Infection/Anal Bleeding?

I am 12 years old…female,and I have had some sort of vaginal infection for two years.It doesn't itch,but I cant control it.It's somewhat yellow and has a bad smell.Last March…I bled while having a bowel movement.It only hapened a few times in about 8 months.Now, for the past couple months //and today// it has happened alot.Why am I bleeding?