Can anyone tell me what this means?

Yesterday I noticed dark brown discharge in my underwear. I have never had this happen before. It didn't have an odor or anything like that. I am also not on my period. I am suppose to get my period in 4 days according to Glow. I have had to pee a little more than normal, but everything else is fine; no odor, itching, burning, ect. My boyfriend and I do have unprotected sex and we had unprotected sex about a week and a half ago when I was ovulating, nothing wild or crazy about our sex. Nothing hurt when we had done it or anything of that nature. Does anyone know what this means? Thank you in advance!