I Am A 64 Year Old Woman, A Health Insurance

I am a 64 year old woman, a health insurance agent just surviving annual enrollment. My hair has started falling out. I'm wondering if it could be due to low thyroid (my thyroid has been inactive for 20 years and I'm on 150 mcg of levothyroxine. Also, I stopped taking any hormones a few years ago, could that be the cause? This just started a couple of months ago but my hairdresser commented about it. Could it just be stress? thank you! Bonny