What Causes Absent Periods With Peroxidase Test Showing 6.4?

Hi, I am 38 years old and always had heavy, very painful periods like clockwork. However, now am 3 months without. My doctor ordered some different tests, to see if I am in my perimenopause. My Hormone level was all good but my peroxidase test was 6.4. She said that is why I am not ovulating. She wants to recheck in 6 weeks.

Yesterday I had some very little brown spotting with a little mucus, but no signs of getting my period at all. The spotting is all gone and I am getting concerned if it could be something different than just a thyroid disorder, please help.