Talk to General Physician on Constipation Severe

Any one help out I'm so much stressed out because of my son 2 years old first he was on meiji fmt after 1.5 years I switch to olperz he started having constipation went to Dr he suggest duphlac 10ml according to his constipation and stool passing. First I start giving 10ml then he pass 3 to 4 stool everyday I switch to 5ml than stopped after 1 month as Dr suggest. Than again he had that severe constipation 2 times he had enema went to another Dr he suggest prulax 5to10ml. But still he's not passing stool.. What to do pls suggest