I Have Had Depo Provera Shot Once In My Life

I have had depo provera shot once in my life I recently got it a second time and I have had been bleeding for awhile now longer than a week?
I want to understand why I keep bleeding the blood is fresh and bright red I do have unprotected sex and I am 19 years old. I am scared that something internally may be wrong please help me to understand what to do.