I've had three term pregnancies and lost all the baby weight (30 lbs the first time, 35-40 lbs the second time and about 25 lbs the third time) and I Ecologically Breastfed and lost all the weight and them some. I didn't gain much weight until I went on Depo Provera when my second one was about 7 and then HRT when my 3rd was about 10 or 11.
Losing the weight is highly dependent on how
Ecological Breastfeeding; feeding nothing but human milk, preferably directly from the breast for the first 6 months at least
feeding on cue (when ever the baby cries) sleeping with or very close to the baby (so that cues are picked quickly and stress hormones don't go into over play due to excessive crying) delaying solids until at at least 6 months
or more, only using solids during the first year when the baby needs them (most breastfed babies need their solids in the afternoon NOT the morning) letting baby self feed solids (baby gets less solids and learns to self feed) allowing baby to set the pace for every feeding, including when to start, when to stop and when to change sides etc are all components of Ecological Breastfeeding. While Token Breastfeeding, (interspersing breast feeding with bottles of formula or pumped milk, early introduction of solids, frequent and long (more than an hour or two at a time) separation from baby in the early months) is still giving baby a lot of antibodies and lots of good human milk and help a lot with bonding, Token Breastfeeding or part time breastfeeding, or short term breastfeeding (less than the recommended 12 months minimum) will usually not result in much lasting weight loss.
This is just the way the female body works. If breastfeeding is prematurely terminated (and up until the last 100 years or so, babies wouldn't live if weaned before the 12 month mark, so the human infant and the human mother are made to breastfeed for at LEAST 12 months, if not more) If the baby is prematurely weaned, the mother's body assumes the baby has not.... survived and keeps the fat so the next pregnancy will give the next baby a better chance at survival.
It's all Evolutionary Biology. No judgements, but it is the way the mother/infant dyad works after millions of years of evolution.