Hi
For now you should you should emphasize on a balanced diet. A balanced diet is a diet that include all the nutrients required by body like Carbohydrate , protein, Fat,
vitamin , mineral , fibre and water.So try to include all the food groups in your diet and don't think of gaining weight for now.
As few calorie and nutrient deficient diet can effect quality of milk and your health so eat healthy and stay healthy.
If you want to discuss further opt for personal chat option.
Meet a Dietician/Nutritionist for personalized diet plan if required
Eat healthy!! Stay Healthy !! As it's the body in which you have to live in!