Never been on birth control before, is this normal?

So the first day of my last period was April 28th, and it was a totally normal period. I went to see my doctor and got birth control on May 12th. I got the arm implant (Nexplanon to be specific). Glow estimated my next period was going to start on May 28th , but it never came. Now, today and yesterday, I've been bleeding but it's been brown - like its old or dried up or something. Is this just a normal side effect of my body trying to expel old menstrual blood? I'm not having any period symptoms otherwise.