Milk allergy?

I’m breastfeeding and think my baby is allergic to something I’m eating. I’ve been reading on the internet and most cases are from products with cows milk in. (I’m waiting for a stool sample of hers to come back) just wondering if any other mums have had this while exclusively breastfeeding?? Never happened with my son and feel bad for her she’s only 6 weeks old just hope she’s not suffering but I know she’s gaining weight absolutely fine and seems mostly happy just has some symptoms of a milk allergy.