What Causes Brown Spotting With No Regular Menstrual Period?

I am 18 years old and when I first started my period in middle school I got it every single month. Then, it became irregular and I got it every six months. Then, I just completely stopped getting it. Around the time, I was in 8th grade and I went to the gynecologist for the first time and they put me on birth control to regulate it (and I started getting it every month). Over a course of time, I stopped taking it and I completely stopped getting my period again. Although, a few months ago I randomly got my period and I haven't had it since. For the past few days I have had bad brown spotting/discharge but no period has yet to come.. is there any explanation?