Hi Vincent,
With time, you will find his pattern to gluten ingestion. It took us a good solid year of attention and looking to find most of the quirks and timing of my ds's soy allergy. We felt we had it down pretty much by age 3. Keep in mind, we were paying attention for a year previous, and had him off soy for another previous 6 months, and knew something was up allergy-wise for about 6 months before that!
The super-obvious symtoms we pinned down before we knew it was soy, but we didn't fully understand the timing of it then. So, I guess it took us about 2 years
Since you already know to look for gluten, you will probably catch on much faster than we did.

Merika