Seriously, the day after endo took me off synthroid my period just went wild. Heavy, heavy bleeding and not stopping. Even after gyno put me on provera to stop it, it still continued. Ended up having hysterectomy couple months ago. Easiest thing I've ever done. So, don't know for sure if it was thyroid or my stupid uterus...but I'm going with thyroid.
Mine is now Day 6 and still going!!!!!!! I am usually 3 days max the past 5 yrs!!!!! I am blaming mine on anti inflammatory meds for ankle .. better not be from Synthroid ... no no no .... in my case I think Mobic med is the cause as it "thins" blood.
C~
I have had very heavy periods lately too, and irregular, since having RAI in June. I hope it goes away.
The syn should help them not worsen them, how long on the syn? It took my periods the longest of all my symptoms to easy and slow back to what would be considered normal menstr cycle, probably 2-3 months being on the syn till they went from 10-12 days longevity to 6-7 days...Good Luck