First of all congratulations. Hope you and your baby, both are doing well. I assume healthy lifestyle means you are looking at weight loss. I hope you are breast feeding your baby. The fat & nutrients which is stored in your body during pregnancy is stored with purpose - to help in milk secretion to nourish your baby.
Next Steps
Your first goal should be ensure the milk secretion doesn't stop / reduce before 4 months.
Water intake is the most important factor to ensure lactation is not affected plus when you are well hydrated you won't be tempted to eat unhealthy food.
Health Tips
Strictly eat home cooked food
Avoid deep fried food at all cost
Opt for tawa fry, grilled, sauteed, roasted food preparation techniques
Avoid refined flour (maida) food items
Eat small but frequent meals