What Causes Irregular Periods In 39 Years?

i m 39 years and had family planning operation after my second child birth about 13 years ago. I m 5ft 4 in height and weighing 60 kgs. I had regular periods all these days but for the last 3 months its irregular and i had my last period about 40 days back. My activities are normal and i have sex atleast twice a week and i m healthy. Please let me know if it and indication for menopause or am i shockingly pregnant.