Congratulations on your healthy boy!!! WOW 4.9kg. You don't need to exercise ... you can just lift him up and cuddle him all day!!

I read in a baby mag (OMG I am not sure it was in a magazine ... I can't remember where I read it!!! ) just last week about dropping kg's after breastfeeding. They said the secret is this:

Don't eat twice as much, eat twice as healthy

Made sense to me
On the exercise, start slowly. Walking with bub in a pram is always a good idea, get your heart pumping and your endorphines flowing ... and burn some fat. Just wait till after your 6 week check-up. My gyne told me I can start walking when I can climb two flights of steps without getting out of breath or having discomfort.

HTH! Goodluck!