Need help with a possible pregnancy symptom...

So I’m on birth control, and wasn’t the best with taking it every day (doubled up a few days recently). Had sex on the 31st on the tail end of my last period. Cut to Monday, the 12th, and I started what I thought was my period, but that would mean it was 12 days early. On top of that, I haven’t had to use a tampon (only a panty liner), and it’s a dark brown/red. All signs are pointing to implantation bleeding, but I’m panicking, and apparently a pregnancy test won’t be accurate for at least 5 or so days (closer to when my period would start).

Please help debunk this? In all honesty, I’m so scared. My boyfriend just broke up with me, and I really don’t want to be pregnant with his baby. To add to that, he broke up with me about a week before it came on, so I’m not sure if it could be stress, or just being bad with my birth control.