Hello I am Dr Mbong,
From what you described, your son seems lethargic & I think it is Ok to be oncerned.
If he is taking medication, the sleepiness may be due to the medication especially if he does not eat much or drink enough fluids. Same for the headaches
. The bug may also cause these symptoms and it may take a while for his body to be ok again no matter how mild the digestive symptoms were.
Is he taking any medication? If yes, which? If he continues being sleepy, please consult a physician.