It looks like you already know the answer. You are doing the right thing. Keep going with the food/symptom journal. Eliminate things that make you sick.
The answer to the second part according to my experience is yes. Some of us who are less sensitive don't want to believe it, but my answer is yes.
Since you are noticing symptoms in response to certain foods, I would guess that it is a reaction and not lymphoma. My mother died of that disease so I have unfortunate experience with it's symptoms.
It is a very foolish person who mistakenly believes that symptoms and damage like this after a strict 10 year gluten-free diet could not be something more serious than low levels of gluten....which has not been established by any reputable Celiac group or intensive medical study. Lymphoma can present as Refractory and anyone that becomes this sick needs to seek medical attention with testing to make sure they are not even sicker than they think they are. They should not take any meds until they rule out the serious stuff. I think all of us can recall Bonnie's posts and what she is going through right now. The doctors blew her off and she was correct...she had a serious problem. Your insistence on everything being caused by low levels of gluten could cost someone dearly. Additional food intolerances should definitely be addressed but downplaying a serious relapse like this is not smart.