Help!

I'm 18 days late. My last day of my last cycle was March 30. The same day I started the pill. I've taken a couple pregnancy tests and they've all said negative. I've felt off the last week or so and then today I had dark brown spotting. I thought maybe I was getting my period, like I'd just skipped a cycle because of the BC, so I decided I would free bleed just a little (judge if you must) to see if the flow increased. It hasn't. Just a few drops of dark brown when I use the restroom. Any ideas?