Hello.
Thank you for asking at HCM.
I went through your son's history.
Yes, they can be due to bug/mite bites (there are several types of bugs/microorganisms, some of them can not be visible with naked eye).
If he does not get welts daily, I would also think of
food allergy. For that, I would suggest you to observe his evening meal and the days he gets symptoms. This will help you to identify a correlation between food and his symptoms.
Were I treating him, I would prescribe him levocetirizine/cetirizine/
hydroxyzine for 5-7 days and to wear loose, preferably cotton-like clothes (to avoid sweating). I would also suggest him to apply lotion like
calamine on his skin.
Hope above measures will be helpful to him.
Should you have any further query, please feel free to ask at HCM.
Wish him the best of the health.
Thank you & Regards.