I could really use some help

okay so i’ve been on birth control for 9 months. 6 months shot, 3 months pill. 4 days ago i took a pregnancy test and it was positive along with 2 negatives a couple days later but it can be because of how early in the pregnancy i am if i am pregnant. yesterday i had sex and started bleeding but it was light so i was told it could me implantation bleeding but this morning i’m still bleeding but it’s a dark brown rustic color and there was a big chunk of something laying on the pad. i’m not sure what it is or if i had a miscarriage or if i was never pregnant in the first place.