Hello Dr, My Son Is 5 Years Old With 15

Hello Dr,
My son is 5 years old with 15 kgs of weight and do not eat well. Last year I consulted a doctor nearby my place and he advised Longifene-A. We have given a single dose of 3 ml for per day for 1 month during nights and he gained a little weight at that time(16.5 kgs). But, now he is back to 15 kgs. He lost his appetite for food during summer season as he used to eat ice-creams a lot. He had motions during summer and sometimes severe stomach pain as well where the doctors said it was just a wind colic and nothing to worry. He is back to school and lost his appetite for food totally.