Hi,
Thank you for posting your query.
Mild 
head injury and 
concussion would not usually lead to repeated vomitings. However, if the vomiting is due to head injury, there would be associated symptoms such as headache, decreased alertness, etc. 
If the vomiting is due to stomach virus, then, there may be stomach pain also.
Please get back if you require any additional information.
Best wishes,
Dr Sudhir Kumar MD (Internal Medicine), DM (Neurology)
Senior Consultant Neurologist
Apollo Hospitals, Hyderabad,
My personal URL on this website:  http://bit.ly/Dr-Sudhir-kumar 
My email: drsudhirkumar@yahoo.com