What Causes Foul Odor Discharge With Spotting?

I am a female. I am about 17 years old and I am sexually active with a guy I have been with for three years and thats the only person. We have had sex with no protection several times and for some reason I have never become pregnant(not that I want to be) Lately I have been having strange smelling discharge and sometimes spotting without being on my period. It has been happening for a few months now. I also have burning while urinating. What is wrong with me? Or is it normal for my age?