Hi Shirley, Good your interested in biology so do I very much!
Often it is mentioned that there are correlations between certain food groups and the suppression of thyroid excretion, its hormones.
They are called 'inhibitors' or goitrogens.
Soy, some nuts, cabbage (cruciferoux), millet
http://www.livestrong.com/article/317239-what-foods-inhibit-thyroid...
And there are some recommendations you can find here:
http://www.marksdailyapple.com/forum/thread48803.html
I would watch out to cut down on a specific foods (and increase others).
This are some tests I would suggest you to look into.