My suggestion is to put a little baby prune juice(diluted) in his cereal or formula/breast milk. Try that a couple of times a day..... for a couple of days, and see if it helps. That's what I did with mine if they ever got that way and it worked. If he hasn't gone within three days I would call his doctor and see what kind of laxative would be safe to give him. I think it's normal for this to happen, b/c his body is getting used to solids(his poop will be different than before). I wouldn't be alarmed unless he seems to be in pain, or doesn't go after the third day. Keep us posted

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Also Krista is right try peaches or pears instead of applesauce or bananas! Hope this helps you!