Usually after delivery, a female should have a body massage and fomentation to whole body. Along with that a blood purifier helps to resume the body fat distribution to normal. Triphala will help you in this case and though it have effect on milk but will not cause any side effect on baby.
But I suggest you to have Maharasnadi kwath along with that as this weight gain is not the regular one.
After examining body constitution and other factors, more proper treatment is possible.
Next Steps
At morning on empty stomach, as well as
after 3 hrs of lunch use waist belt. Remove it before taking meal as well as before going to sleep.