constipated 4 month old

ok, so he's not fully comstipated, but his poop is hard and he can't hardly poop. I have to help him push (I just bring his knees up and GENTLY push them to his tummy). He's pooping everyday, but it's always hard at first. The doctor said that hard poop in babies that young is a sign of constipation and to try prune or apple juice in his bottles or cereal (yes, I'm feeding him cereal at 4 months - it was recommended because his bottle wasn't satisfying him). But the juice doesn't seem to be working very well. It's kind of helped a little, but not really. And we've tried every kind of formula there is and he does best on what we have him on now. Is there anything else I can do for him? I just feel so bad for my little man. He acts fine other than when he's trying to push, so I'm pretty sure he's not sick or anything... just can't poop  

rice cereal tends to make babies constipated. talk to your pedi about switching tooatmeal instead of rice.

Gerber makes and oatmeal cereal for babies

thank you for that information. I didn't know rice cereal had a reputation of making baby's constipated. I'm gonna call the doc office and ask!