3 week old constipated

Changed my baby forks milk to dairy free last Sunday (with advice from my doctor) as we think she had a cows milk allergy, she is still suffering with trapped wind but hasn’t cried for long periods like she was (still cry’s out in pain though) however she’s now constipated and has had two solid poops tonight, it’s fine from her only going every two days to now been constipated, could it be the milk? Does this mean us not a cows milk allergy? What do I do? Shall I ring the doctors again? Sorry I’am a new mum and feel like I have no clue what I’am doing