I wouldn't worry. With #1 I got my period back when she was 4 months old and was exclusively bfing.
With #2 I got it back at around 20 months.
This last time I had a nasty surprise and it came back at 13 months. I had no PMS like symptoms and had no idea it was coming. Literally had nothing in the house to help deal with it until I sent the hubby to the store. What a day that was!!