Early period???

I had brown spotting at 9dpo which I thought was IB, until I started getting severe cramps that night. Woke up to a full blown heavy period. Heavier than I have had for a long time. Assumed it was AF coming 4 days early but the thing is my temperature has only just dropped today (day 4 AF). Has anyone experienced this? Can anyone shed any light on what's going on with my body? I came off the pill in November. Is it just my body adjusting? Any suggestions would be appreciated!