I am thinking that you had a past infection, and developed a sensitivity because of the body's memory of similar antigens contained in food.
There may also be other factors contributing to an already present condition (and there are so many they couldn't even be listed here).
But overall, you are looking out for yourself, and it sounds like you're in good hands.
I would avoid going into any strong medications, and try and focus on the types of food that might upset your gut, especially food groups known to cause sensitivity.
Check to see if your refrigerator is producing the right temperature (Google it). It sounds like you are healthy, but if things start to get worse, then keep a good record of your new symptoms.