Hi , green coffee beans contain chlorogenic acid which helps in reducing weight but it also contains caffeine which when taken in large quantity may cause some problems.
So you can start with safe dose -250 mg -350 mg per day of green coffee extract for 10-12 weeks.
Breastfeeding doesn't cause weight gain.
Next Steps
focus on diet and exercise ,that will help you more in reducing weight.
Health Tips
avoid high fat and simple carbohydrate foods. take 5-6 small meals instead of big and heavy meals