I'm aprox. 12dpo and i think i started my period today except it's spotting and it's mostly brown with red mixed in. what could this be?

Be patient: 12 days post ovulation means that you are at day 26 in a typical 28 day cycle. Brown blood is just slow or light flow. It is possible that you are going to get a period or sometimes this is implantational bleeding. If the bleeding remains lighter than usual do a home urine pregnancy test on first morning urine on about Day 31.

Wait and see. : Wait and see if it progresses into a real period over the next couple of days. If not, check a pregnancy test.