squeaky, you make a hell of a lot of presumptions!
My diet wasn't bad at all. I had hyperemesis during pregnancy and initially lost a stone (both times), but was then ^ravenous' in the third trimester and while breastfeeding. I was HUNGRY, so I ate and yes, I gained weight.
'I cant understand that logic at all.' Really? Its not that complicated. During the first months, I was breastfeeding and dealing with sleep deprivation. My priority wasn't my figure, it was my baby. When I went back to work after about a year or slightly less, BOTH TIMES, I started exercising again, I was generally more active and my diet changed, as I wasn't at home, sitting on the sofa, breastfeeding and ravenous. Guess what? I lost weight.
Honestly, its not that hard and in fact, its what happens to most women 
I am 35 years old and slim. I had my kids at 28 and 30. That was a 2.5 yr period maybe where I was a bit porky. Its not the end of the world, surely?
OP, have a slice of cake and ignore the misery guts