9dpo brown spotting

Elizabeth • 26. Married to my best friend. Have 2 amazing sons Nathan (9/8/13) and Oliver (5/27/16) and a little lady Annabel (5/9/18)
So I have not had my period since my son was born 13 months ago. Going based off CM and CP I'm pretty sure I ovulated on the 20th. I woke up today with brown spotting. Could this be implantation bleeding or most likely my period?