What Causes Spotting In Menopause Period?

I was taking birth control pills for many years. I suddenly went off them and wasnt getting my period( for about 2-3 mos), so my dr did a blood test to check for menopause. It showed I am in menopause and he said I wouldnt get any more periods. a month or so later, I had some spotting. the next month, I got a regular period, actually a lot heavier than normal. so he told me to go back on the pill. whats going on? is this normal? I'm 45