Are you sitting down?

- Cuz you could very well be experiencing some perimenopausal symptoms.
Hormones start to make small adjustments as you're approaching full menopause, and it can be rather erratic. It can start even 10 years before you actually enter menopause. This is just ONE possible reason.
Your BC could very well be doing it, too. Is this a new method you are using? Talk to your doctor, if so.
Also, loads of women in your age group have battles with their libido. Just ask some of the guys on here

Even the most sensuous in nature can really struggle with their desire to stop everything (let's face it - we're living VERY busy lives

) and hop into bed.
I'm sure others will have some good reasons for you to think about, as well.