Molly,
  It's certainly possible for a milk protein allergy to only cause gastrointestinal problems.My daughter had chronic constipation from the time she was an infant--and all doctors wanted to do was give her more laxatives. We tried just about every kind, and at one point she was on the adult dose+ some (when she was a year old). I got tired of the mentality of laxatives for life, and did my own research, which turned up two journal articles, one from  the New England Jounal of Medicine, and the other from the Journal of Pediatrics which were clinical studies which found milk protein allergy to be a major cause in unexplained chronic constipation in infants. Armed with those, I took my daughter to an allergist, who tested her for the protein allergy--which she had. We've eliminated all dairy and seen tremendous results. 
   
  In addition, there may be symptoms of milk allergies that you wouldn't suspect. Some researchers and doctors believe that milk allergy is a major cause of ADHD and behavioral problems in children. I can certainly see a difference in my own daughter's attitude and demeanor when she is exposed to milk.

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  " I had never heard of a dairy allergy that 
produced symptoms of diarrhea, bloating, and pretty sever pain that wasn't 
lactose related. "