My DS is 3weeks old and has been formula fed fo...

My DS is 3weeks old and has been formula fed for 2,hes on karicare and having major pooing issues,hes grunting and going red and only going every 2nd day,yesterday he did a small pellet like hard nugget and it was awful,i dont know what to do,i had the same issues with DD and she also ended up with eczema too,ive been doing some research and it seems Nestle do a formula especially for easy to digest and allergies,im just not sure whether to change,it says its easy to digest which is the most reason im leaning towards it hoping it would help with the constipation,its called nestle nan HA gold has anyone used it and had an good results?Im at my wits end i dont want to go threw this all again its mainly about the constipation issues at moment but i just read that if one child has allergies then this formula is also good for second child incase they also get eczema i just dont know whether to stick with the formula ive got and just hope he works threw it or to try just another brand or?Its also a dearer formula which i dont mind but if its no different to any other i dont want to be sucked in,please any advice at all!!