I'm Taking Synthroid For Hypothyroid. I Had My Last Period

I'm taking synthroid for hypothyroid. I had my last period over 5 years ago. I'm 56 yo. I started bleeding over a week ago. It has slowed down to very light now, but am wondering if it could be that my medication isn't working? About 20 years ago when I was having some major period issues of heavy and very long periods my obgyn did an internal ultrasound and a uterine biopsy, after not finding anything except mild endometriosis he ran a complete hormone blood panel and found that my thyroid was not really working very well. After being on the medication for a couple of months and some medication adjustments the bleeding went back to normal. Could it possibly be the issue again?