One immediate reaction you could get to anything that you allergic to is mucuous production. Did you experience any mucuous production after eating buckwheat? Did you experience any kind of “burn” symptom after eating buckwheat?
What else was in your burrito?
The gas could be from constipation and the cramps may not be related as well. I take a supplement called zypan which reduces or completely eliminates any gas problems.
Since you are still experiencing die-off symptoms, you may want to wait a few more weeks before trying buckwheat, it is up to you; but it could just be coincidence.