It is important to seek the advice of your doctor before beginning any physical activity, especially after a cesarean section. Yes, you can do asana after 4 months of a c-section, but even then, you should consult your doctor before beginning any exercise regimen. Make sure to start slowly and pay close attention to your body's response. If you feel any pain or discomfort, stop and consult your doctor.
Yoga can be a beneficial form of exercise to help strengthen the abdominal muscles and restore the core strength that is needed for everyday activities. However, it is important to take a slow and gradual approach, and to start with poses that do not put too much strain on the abdominal area, such as gentle stretching and breathing exercises. As you progress, poses such as cat/cow, warrior I and II, and seated twists can be beneficial. It is important to listen to your body and take your time to ensure that you are not pushing yourself too hard. Also, for the first year, it will be advisable to dedicate your time to the nourishment of your new born baby. With the diet suitable to you and your baby, the hormonal effects responsible for such marginal overweight during pregnancy shall normalize itself within a year. Meanwhile, alongwith above mentioned stretching exercises, you may practice few of the suksham vyayam for your over all fitness (in consultation with your doctor) that suit your capacity and remember that you should do within your limits and no need to practice those exercise which appear difficult.
Related Question: Pranayama after 3.5 months of C-Section.