Do not drive yourself crazy eliminating foods, getting testing, etc.. Research it, many, many boys (and girls) have this problem and they do grow out of it. My son was probably 13+ before he grew out of it. My dad was the same way, and I had issues, but not that severe. Of my four boys two had this problem. The other was about 8 or 10 when he stopped. I did use the alarms, which woke me not him. Then I used one that vibrates when he was older and that did help the one, but the other just took longer. Just do not punish him, help him to understand that the alarms might work, but never to be upset by it. Mine both wet the bed in the early morning hours around 5am, after being dry all night. Do yourself a favor and let them wear Pull-ups they are a Godsend! If you want to work with an alarm, be prepared for sleep dreprivation on both parts.
About me: SAHM homeschooling last three, one boy in USAF, one boy going into USN, 2 boys ages 17, 16 at home and one girl, 15.