Hi there, you are through to Dr. Jake. Im a UK based vet. Im sorry to hear of your concerns with your dog sherwood.
Vomiting/diarrhoea is a common symptom in dogs that we see on a regular basis. it can be cause by many underlying conditions. which i will explain below.
The most common cause of vomiting in dogs is gastritis or gastroenteritis. this causes vomiting and or diarrhoea. once of the most common reasons for this is dietary indiscretion- they have eaten something that the body doesnt agree with. if this is something which persists for more than 3-5 days then there might be a suspicion of an underlying allergy or food sensitivity- in dogs the most common is to chicken, beef and pork. with dogs that have suspected underlying allergies that cause gastrointestinal signs we recommend using a specific diet called a hypoallergenic diet. this has allergens removed so it doesnt cause the gastrointestinal issues seen. its very important that they eat only this diet and no extra treats or snacks as this can cause a flare up
another common cause of vomiting in dogs is ingestion of an object that isnt digestable and leads to a blockage of the bowel. foreign bodies can lead to regular vomiting/ diarrhoea, not wanting to eat, lethargy and abdominal pain- they are generally vomiting regularly and look quite sick with this so i suspect this is less likely
another condition called pancreatitis is common in dogs which is inflammation at the organ, the pancreas - this is involved in digestion and often gets inflamed by, again, eating food which is high in fat. this also causes vomiting +/- diarrhoea and abdominal pain.
other conditions such as liver and kidney disease can cause vomiting though i wouldnt expect this to occur in a dog his age.
as he has is quite young and had the symptoms on and off i would recommend making an appointment with your local vet for examination- if he is quite bright eating and drinking then this should be ok to wait until after the weekend. they will be able to conduct a full examination, making sure there is no signs of dehydration, they will be able to feel his abdomen to make sure there is no pain here and possibly feel if a blockage is present. your vets may recommend blood tests and imaging in the form of x rays or ultrasound if they feel necessary and can provide medications to stop the vomiting. if they are happy with his status they may treat him with medications he can have at home to resolve the signs
i hope all this information helps