I'm happy that you have asked me to assist you with your child and hope that you can benefit from my many years of helping parents like you.
This time of year there are always stomach viruses going around and that is most likely what he has. At his age he is prone to get dehydrated and if his skin is pale, he is cold and at all lethargic or doesn't want to stay awake then you need to take him in to a doctor or A&E now to have him examined. They can test him for dehydration and give him an IV to help him immediately feel better as well as prescribe a medication (ondansetron) to keep him from throwing up so much.
For now just stick to clear liquids and no milk or foods until a clinic or doctor looks at him.
Thank you for the reply, can it be food poisoning? He also had a fever of 39C about an hour ago, which is going down due to nurofen.
It could be but doubtful with fever and food poisoning is really not all that common.