How To Improve Appetite In A Child?

Hello Dr, My 14 month old son is just not interested in eating and theres nothing that I can say that he likes. These are the details of my son: birth weight: 3.4 kg current weight: 9.6 Kg i am trying to give all type of food like, rice, curd, wheat bread, fruit but he always avoild all foods. Breast feeding is also stopped. He is also suffering from constipation problem. Is there anything to increase his appetite? Thanks,