16 mo bf breasts keep shrinking

Ugh I'm so down -I was a full c prior to bfing/ d-dd when pregnant and starting at about 10 mo pp breastfeeding my breasts started shrinking- I am underweight but now they are barely a b possibly an a -I'm now 16 mo pp still breastfeeding and everytime I look in the mirror they look smaller - I thought this wasn't supposed to happen until after breastfeeding - I don't get it. I feel self conscious about it as I loved my boobs before - why would this happen during breastfeeding?