Could The Light Periods Be Due To Pregnancy?

Hello, I am 47 years old, and have been having very light menstrual period for the past year or so. It's rather on a regular side, coming every 27 or 28 days. It's always heavy before I had my large fibroid removed two years ago, but since then, it's always been light, lasting two days. I don't have any symptoms of menopause at all (hot flash, insomnia..), and every time my menses come, I don't even have any PMS symptom or spotting. I got pregnant (but ended up in a miscarriage) 10 months ago, even before I got pregnant, my menstrual period was always on a short side. What could be a problem? Thyroid? I appreciate your help.
Thank you. Tuyen Tonnu