Hi. I have a four week old, he has been bottle fed for two weeks now. i've been using Esbilac milk replacer, I went to use the next step, and it seems to be bothering his belly, after he eats it he throws it back up. So i tried going back to the milk and now he dosn't want to eat. I also tried mixing the two and he is still getting sick. Any help would be greatfully appreciated, Sue.