As a nutritionist/naturopath I can tell you that not only is gluten sensitivity not
rare, but it is growing
segment of the population. And yes, a round of antibiotics is enough to wipe out the digestive flora and make digestion nearly impossible for a few weeks. During that time, damage to the mucusal lining of the GI tract can occur, and that damage will take time to heal. Once damaged, protein structures like gluten and casein (found in dairy products) can and do become very problematic.
Some people, as is the case in Celiac disease, develop autoimmune disorders and must permenantly remove gluten from the diet. In other cases, it's just temporary.
As the manager of a healthfood store I can tell you that we exist to carry alternatives for people who cannot buy their food in a regular grocery store. Conventional grocery stores do not understand the need for alternative products, often do not carry the correct products, and the staff does not have enough knowledge to walk a newly diagnosed person through the process.
CHECK OUT YOUR LOCAL HEALTHFOOD STORE. The staff will be well educated in this topic.
AND VISIT A NUTRITIONIST OR NATUROPATH, not a medical doctor or dietitian. They are not trained for this! When a condition is doctor-caused (by antibiotics, in this case,) the medical establishment is not going to admit there IS a problem, much less be trained in what to do about it!