Candida could be the culprit but there could be others. The GI tract is a complex environment where lots of things live and it is the most vulnerable in terms of infection, which is why it is important to make sure we practice good hygeine (wash fresh fruits/veg in some type of sanitizer, cook foods to temp etc).
A big portion of immunity resides in the GI tract. The food sensitivity issues are likely reactions from the immune system. When infection is present, it activates the immune system and it becomes overactive and dysregulated. Leaky gut comes around due to the immune activation which damages the lining of the gut.
The anti biotics could have wiped out beneficial flora. Pre biotics may be a good idea such as apple cider vinegar, kefir could help as well. You have to observe reactions. Nutrients play a big role as well. Vitamins A, E and D help the mucous membranes, so it may help the GI tract.