Help please!!!!

Sheila
I have pcos for several years know and im trying so hard to have a baby ive been so irregular but since my doctor put me on metformin 5 months ago i started getting my periods on time the first month after metformin i got my period so i stoped metformin and know 5 months straight i have had my period on time this month i had my period on the 7th and ended the 11th know im on my ovulation week i had sex on the 17th and myfertility ovulation said start 24th  so i did my first day 24th and i did yesterday 25th and today im bleeding a pink color/brown i took a test its negative what could this be?