I need some help 😳

I ovulated on wed 15th I used preseed and BD 3 times that night...next morning I had a negative ovulation test and it was negative I still BD tho....now since Monday I've been spotting but is very little like a quarter size all day...thing is the blood is very dark also when I pee sometimes there's little strings of blood and not blood cloths...any idea of what it might be? Also I took a pregnancy test last night and it was negative 👎