My son got sick after drinking this milkshake

My son drank Crystal Vally milkshake an about 15min after drinking the milkshake he started complaining about stomach ache and then started to vomit, this happened last night at about 20:00 is is now the next morning and the vomiting hasn't stopped. The use by date on the bottle is 02/10/2015 I am convinced the milkshake caused it but I might be wrong. He didn't drink or eat anything else out of the ordinary, please advise...