This started this past Saturday...

I knew I was going to start my period soon since I was getting close to the end of my birth control pack (Brown Pills) but never felt my period coming. No cramping or anything. Well Saturday came and I notice brown spotting and something came out and I have had a really bad headache and back pain. I take mortin and it helps for a little but never really goes away always comes back. Could the thing that came out be a tissue and I am just pregnant. Help!!!!