i suggest you get further investigation into the problem by getting a allergy test, that away they can test out up to 40 to 60 allergy producing agents, it may have even been food related or yes medication related have you looked at the side effects of his drugs? What has he been eating? Think over these possibilities.
http://www.allergynursing.com/questions/testing1.html
I hope i have helped do let me know if i can be of more assistance to you.
