My post-baby belly goes away after baby turns 4-5 months and able to fit back my pre-pregnancy jeans. Actually for me I did nothing, just fully breastfeeding and eat healthily (less sweet, less meat etc.).
However, you can do some exercise to get rid the post-baby belly. http://www.fitpregnancy.com/exercise/postnatal-workouts/5-exercises-your-post-baby-belly
Alternatively, there are some fitness class designed specially for postpartum mothers:
-http://www.body-by-rick.com/singapore_pre_post_natal_fitness_programs.htm
-http://www.ezfit.sg/pre-post-natal-fitness-training.html
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