selenium was helping.. now its not

so I posted on here 3 months ago that my dr suggested selenium supplement for my thyroid to reduce inflammation. WELL amazingly, I had 3 periods that were *normal people discomfort* and the only thing I changed was taking selenium. I thought wow this is a miracle!!! well now I started af today (☹ 8 months ttc) and the pain is unbearable again. I haven't stopped the selenium. and I've even been eating healthier. why would my symptoms get better, and now back to worse??!!! feeling lost. I have a dr appt next month.