Hi I Am A PCOD Patient And Have Been On

Hi I am a PCOD patient and have been on meds since the last 2 and half years my doctor advised me to switch between two medicines I.e Diane 35 and Deviry after every 3 months .However it seemed that my periods were finally on the track but since last 4 months I have hardly bleed my periods won’t last for more than 2 days the flow is scanty,and with the recent period it got worse it’s only brown blood
What could possibly be the reason for the change