The little bulge you sometimes see on skinnier girls after they have just had a baby is just their uterus, which takes about 3 days to contract down after birth to its original size. Also your skin can feel soft and squidgy (which i loved, it was so cuddley hahaha) but that just goes quite quick with general excercise, simple as walking xx
...I didnt put on any weight with my pregnancy with my twins, I was ALL bump, you could still see my skinny ribs poking out above my bump, and I was still in size 8 jeans haha, so for me I didnt have much to lose
JUST TO ADD - I did move house the day after giving birth, and I had to walk 3 miles uphill and back again twice a day to visit my babies in SCBU cos they were premature, and I had to go shopping to buy blankets, clothes, nappies, cots, etc, because I was homeless in my pregnancy so didnt have anything ready, and also they were early so I was quite unprepared lol! I didnt have a choice really, but it is just ridiculous trying to do any excecise and lose weight or anything straight after birth, so even if you look like a moose after birth, just leave it a while before rushing into losing weight, I'm not saying you will, but some people do
