What Causes Vaginal Spotting?

I am 43 years old and have been told by my GYN that menopause is several years away. Last thursday I started spotting deoxygenated blood and have not stopped. It's not time for my cycle. I did have an episode back in sept where I did this for about a week and then had a period for two weeks and the dr gave me hormones and got me back on track. What could this be coming from and should I be concerned?