Hello thanks for asking from HCM for your health related queries I can understand your concern. Though based upon the query its difficult to find out the exact diagnosis but his behaviours like fear from children of his age group, crying spells, not mixing with children suggest some thing like anxiety. In my opinion there is need for evaluation by a psychiatrist. Its not common to have anxiety at this age but sometime underlying stressor in baby, fear from anything can result in similar symptoms. As you have mentioned that he responded to Fluoxetine so consult his doctor again for re-evaluation and to start medicines again. In most cases the medicines help to reduce the symptoms and he will recover from his fear. This will help in regaining the weight also. Consult a psychiatrist for prescription of the drugs. Thanks, Hope this helps you. Take care Dr. Seikhoo Bishnoi, Psychiatrist