K.S.
Are you sure it was the Tuna? anything you ate in the last few hours could be the culpret. I could not eat corn while i was breast feeding. Daughter could not handle it. It takes a few days for what you have eaten to cleanse out of your system. But fish is a common allergy. When my daughter had an allergic reaction we did take her to the doctor but they said they could not really do test till after 2 years and 4 years because you get a false result. Also did he get bit by an ant or something while he was sleeping? Sorry gave you more questions than answsers but I went througgh this and we had to slowly rule out items. But a call to the doctor will ease your mind.