Similac Alimentium

My little guy was getting very difficult with both regular formula and Similac total comfort (non-stop crying, gassy, diarrhea) so my pediatrician recommended that we try Similac alimentium... Since then the fussiness is gone but he eats a lot less, a lot more often... With regular formula and breast milk (he was breastfed for 3 weeks), he was regularly eating 4 oz every 2-3 hours. Now with the alimentium, he eats anywhere between 1 and 3 ounces, and cries for more food ever 1-1.5 hours! He also sleeps less (used to go for 3.5 hour stretches at nighttime which are now down to 2). He also looks completely disgusted whenever he eats... He is 4 weeks old, and started the Similac Alimentum 3 days ago. Has anyone else had this problem? Is this normal?