Hi,
I had a baby 21 months ago and I still think that my periods are returning to normal, if possible. Then I realized that maybe i don't know what normal is because I was on the pill for a period of time and then I was so focused on trying to get pregnant, that I don't think I was paying attention. Mine are lasting for a longer time span then they should. I will mention it to the Dr again, but in year's past, they never seemed to have a clear answer. I did read that it can take many, many months for a period to return to "normal". Maybe they will do a trial of birth control to see if that reset everything. They did this for me at once point..I think. Good luck! I am sure it's fine and will work out...of course a good sign that the sono was clear. Maybe some hormone bloodwork?