high fertility reading but my period arrived

I'm so confused. Been testing for ovulation, have had 8 high fertility days (no peak) and today my period has arrived, 10 days early?! Normal period cramps etc. Cycle is usually 24-28 days (varies occasionally) I've started taking supplements about 3 weeks ago. Does anyone have any suggestions/experience of this. I'm also still getting a high fertility reading today! Any help would be much appreciated