Asthma is commonly caused by allergic reaction of the body to some substance leading to inflammation of the lung lining. Here histamine is released as it has a role as in inflammation. It also affects blood vessels may be causing headache and easy bruising. It is also associated with mental health like schizophrenia and obsessive compulsory disorder on long-term. Good news is that Vitamin-C has anti-histamine effect so it would be advisable to give him vitamin-c rich natural fruits. But as this diagnosis goes to molecular level so it still needs evaluation of blood histamine level. Other wise on more practical grounds, I would advice you to consult your family doctor for blood complete blood picture to rule out any blood dyscriasis (leading to bruising) and mental stress to your child due to which possibly he may be causing self-inflicted injuries (for which he may be not conscious about) or blood and headaches could be due to persisting asthma.