I was on a low carb diet and did not eat any breads for the past month and I felt great! my stomach pains, bloating, and constipation, and lethargy went away. As soon as I began introducing bread in small amounts back into my diet, I started to get the same symptoms again that I have had my whole life. Could this be an allergy to bread, namely wheat?

You could have Celiac's disease. It sounds more like an intolerance than an allergy to me.