What Causes Irregularities In Menstruation?

I am starting menopause - my periods became irregular several months ago. I had a regular period, then nothing for 3 months, then a monthly period for two months in a row - I'm having the second one now. My question is: this period was very atypical. Twice I had a gush of clear liguid along with blood and the whole period was heavier than I've ever had. What's going on?