Light brown spotting

Kat

Hello! I took letrozole for the first time this month as my cycles have been very long and unpredictable. I am on day 3 of very light brown spotting (almost discharge looking); spotting came 12 dpo. In theory should be getting my period today (14 dpo). Could this be implantation bleeding or just a very light period due to the letrozole? Only other symptoms I’m experiencing is a breakout on face and slightly tender breasts. Pregnancy test says negative. Thoughts?