I recently began giving my 11 yo lactaid (store brand) because we...

I recently began giving my 11 yo lactaid (store brand) because we noticed he had a problem with gas and diarrhea after eating dairy. Tonight he had 2 tablets with dinner and about 2 hours later complained of his stomach hurting. He sat in misery for about another hour and a half until he finally vomited. He also had diarrhea. He seems fine otherwise (no fever, doesn't feel "sick") and after reading all of these stories after doing a search I'm thinking that this must be what it is. I feel terrible as a mom giving it to my child and making him feel so horrible!