It's not really normal, but it's not too surprising. Most likely the spotting is due to the fact that you haven't ovulated since your miscarriage. Ovulation is what causes normal periods, and when a woman doesn't ovulate, irregular periods or spotting is common.
It's not unusual to not ovulate at age 45, even if you have a history of very regular periods.
I would recommend that you see your doctor, just to check things out, and also to take some progesterone pills, which will stop the spotting. Then, hopefully you'll get back to fairly regular periods. Best wishes.
Thank you for your payment and rating.