Constipated 2 1/2 month old

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So my baby who’s now 2 1/2 month old was constipated for 3 weeks with no poop at all he finally went yesterday the Dr was concerned and of course So was I. So I don’t know if anyone has ever gone through that they told me it’s normal can be up to 2 weeks for breastfed babies but 3 weeks no poop was worrying me , and honestly still is . He has his follow up appointment Friday and see what happens , he was prescribed a powder like a laxative but didn’t work the first try and he finally went . He has very stinky gas smells horrible . Has any moms experienced that for this long ?