Hi, my son is three weeks old, I fed him nan perlagon the first week, he became constipated some nights it wkukd be so bad, he would cry through the night, the paeditrician suggested that I change the formular, so the second week I gave him nan optipro, he kept vomiting it, and it would even come out through his nose everytime he vomited, so I am now giving him lactogen, he does not vomit it, but Today he is constipated badly again, what can I feed him?