Sorry this is late…but I have experienced something like that as well. Normally I eat green onion. I guess I like the flavor a little better. I had some white onion a few weeks back and noticed a slight burning feeling in my stomach. When it happened, I just thought it was because onion is an antifungal. I didn’t notice any other reactions other than the burning.
Curious if you figured anything else out on is since your post?