I am a 45 year old woman having periods every 21 days like clockwork. I have just started seeing a very special man and sometimes these frequent periods get in the way. How do I avoid an unwanted period when I want to.

I don't think you can avoid the cycle. But you can avoid him when it happens. I guess you are coming up to menopause and that is a blessing in a way. After menopause a whole life without worry is opened up for you, sexually.