I Have Breastfed My Baby For 1 Year And Am

I have breastfed my baby for 1 year and am weaning. I currently breastfeed about once a day. I am on the minipill and I am getting ready to switch to the regular pill. I got my first period on June 30-June 24. I also had bleeding on June 30-July 4 and light brown spotting on July 13-15. On August 16 I had pink cervical mucus when wiped but it was only once. I went to the doctor on August 21st and she told me that I should become more regular overtime but it has been 54 days since my last period. I had a negative pregnancy test last week. What other causes could this be from.