Dr. Valentine Enemuo, M.D

Constipation is very common at this age. While about 5% of patients with dairy intolerance or allergy can present with constipation, it can still present in this age group for other reasons. Excluding milk for 2-3 weeks from his diet can help you exclude milk as the cause.
However, dietary changes with increased fiber, and fluid intake can help. If no improvement can consult with a Pediatric gastroenterologist for treatment with medications such as miralax.

Adequate fluid intake daily helps good gastrointestinal health. Good oral hydration and fiber intake daily will help prevent constipation.

Colic does not have any proven treatment. However, there other diseases in infant that can present as colic such as gastroesophageal reflux, and milk protein allergy.
Treating gastroesophageal reflux and making changes to the feeding such as mom avoiding dairy, and sometimes soy if breastfeeding, or changing to semi-elemental, or amino acid formula can sometimes help.

Psyllium Husk is good, but has to be taken with adequate oral fluid daily. Ensure he takes adequate amounts of fiber daily.

Lactose intolerance is not associated with physical weakness. It might affect his activities indirectly because of abdominal discomfort, bloating, gassiness, and diarrhea. However, taking lactose-free dairy will eliminate these symptoms effectively. There are lactose-free dairy products in all stores, including lactose-free cheese, milk, ice cream, etc.

Probiotics are generally safe at any age. There is no evidence that a probiotic daily is associated with a healthier gut. However, a good diet will promote the growth of good bacteria in your gut associated with a healthier gut.

Constipation is not normal in children. However, it is common in children. 25% of a general pediatric gastroenterologist practice is constipation, while 3% of general pediatrician practice is constipation.

Skin rash with blisters and itching that is usually bilateral, known as Dermatitis Herpetiformis is sometimes associated with celiac disease. Although less common in Pediatric population.
The symptoms of celiac disease include diarrhea, abdominal bloating, gassiness, constipation, poor weight gain, weight loss, nausea, abdominal pain, dermatitis herpetiformis, bone pain, joint pain, short stature, weakness, tiredness, seizure, numbness, headache, infertility.
Celiac disease can be confirmed by a Pediatric gastroenterologist with upper gastrointestinal endoscopy with biopsies (tissues) taken from the surface of the small intestinal lining showing damage to the lining (villi) after the screening blood test showed elevated anti-tissue transglutaminase antibody (TTG).
The skin rash of dermatitis Herpetiformis is diagnosed by a dermatologist with skin biopsies (tissues) of the rash showing the typical damage of inflammatory cells and deposition of IgA.