Hai im dr.hema physiotherapist. I had gone through your query. During breast feed its normal to loose weight, and few mothers find difficult to gain weight even after the same is stopped. Any Unintentional weight loss doesn t always have an underlying cause but it s oftenthe result of one of the following: 1..depression, lack of sleep. 2.anoveractive thyroid gland(hyperthyroidism) 3.over-treating an underactive thyroid and any illness. So its important for us to rule out for safety sake and as you had mentioned day by day your weight is reducing. So you required blood investigation and thyroid profile checked discuss with your gynaecologist. In mean time start taking healthy fat and follow a good diet. Consume more of natural diet like fresh fruits, green vegetables, whole milk, eggs, wheat,nuts, banana (less water contentfruit with more carbohydrate), dry grapes, yogurt, Olive oil in salads, cereals for breakfast. Try to eat six times a day, with each meal (or at least three of them) containing protein, starch, vegetables and nuts. Your diet should be rich in protein, you can go for protein suppliments or protein shakes. A sample meal would include a turkey sandwich on whole-grain bread with mayonnaise and tomatoes and a fruit smoothie.Eat often and choose wisely, and you can expect to gain an average of half a pound to 1 pound per week. Avoid oily and junk food. The right combination of healthy food, exercise, right breathing, rest and sleep must increase the pound. Hope the information will help to guide you. Im doubt do reply.