Breast feed made me fat

Hi all .I had a doubt on breastfeeding.for my first kid I was breastfeeding on demands I also gave formula cause my milk is not enough for him.i put lot of weight around 30 kgs at that time I just lost 5 kgs .baby is 3.5 kg.i didn't lost my weight from there .after I stopped giving bf I reduced my weight and back to pre-pregnancy weight that is after 16 months.now my question is how can I reduce my weight while breastfeeding ? Is there any good suggestion? Ofcourse every one is different . somebody will loose their weight immediately somebody will not .but I want to try something new this time.becoz I missed my pre-pregnancy body .this pregnancy I started at 64 kg and now I am 80 kgs .I don't have gd.but idk y I put this much ...I walk for 4 day in a week for 30 mins.seriously I want to reduce my weight atleast 20 kgs