Dark blood

I missed three bc pills around a month ago.  I took my pills same time every day. I've had sex with condoms on everything I've had sex since then. About a week or so ago I had bleeding a week after I finished my last period. At first the blood was scarce but after a few days it was kinda heavy but very dark brown with a lot of thick clumps. I'm very paranoid it was implantation bleeding but it could also mean that the hormones are adjusting with the bc. According to my period tracker app I'm supposed to get my period tomorrow and I took a pregnancy test today and a few days ago (an early pregnancy test) and they both came back non pregnant. I'm an anxious person so if you could give me an idea of what might be if going on, it would be great