Should I Take A Pregnancy Test While On Depo?

Hi i just want to know ive been use depo 6 months didnt go back in july for my shot had unprotected sex the week after last week ive been getting headaches,backaches that i can almost cry sharp cramps that comes and goes went to clinic for pregnancy test that was negative.last week saturday i went to toilet wipe there was light blood only wen i wiped last nite i felt some discharge coming out went to bathroom wiped and there was brownish on the toiletpaper so im very cornern now because my stomach is tight and i dont know if i should take the pregnancy test because im off depo one month now and when i count the days when last i had sex its 3weeks