A. Since it is a new problem, it is hard to tell what is causing it...
If a lot of other kids at school are sick with a cough or vomiting, then he may have a simple viral infection that will hopefully quickly pass.
If he has not been around anyone else that is sick and doesn't have any other symptoms, then it could be something he ate that is disagreeing with him. I wouldn't think that it would be your breast milk though, unless you have been eating some new foods that you haven't had much in the past.
If you do think it is something in your diet and his symptoms linger, then you might try eliminating the common 'problem' foods from your diet, such as:
- milk and dairy products
- spicy foods
- gassy foods, like cabbage and broccoli
- foods with strong flavors, like garlic
- 'allergy foods' - eggs, peanuts, shellfish, wheat, soy
Whether it is something you are eating and that is passing into your breast milk or something he is eating, a simple diary might help you find a food that is causing the problem.
Do talk to your Pediatrician and/or a Lactation Consultant before eliminating too many things from your own or your toddler's diet though.