Thank you for sharing your question with the EmpowHER community.
Menstrual symptoms can be similar to pregnancy symptoms. Since you've had several negative pregnancy test, one which was a blood test, it is likely that your hormones are imbalanced due to missing two birth control pills and doubling up on them once you realized you missed.
The 3 days of red/brown show for 3 days was your menstrual cycle, even though it was light. It's normal for your menstrual cycle to be irregular after missing and getting back on track.
I hope this helps.