Highly unlikely. First, there's no way steroids make your immune system so weak that you get infected with candida albicans (the yeast that does this). Second, very unlikely that you were colonized from injection.
The people that esophagitis from candida are AIDS patients, and cancer patients who are very sick and near the end. I'd be interested to see your CBC with a differential to see how your immune system is responding to this. Your doc is lazy if he is chalking this up to steroids he should make his differential broader and be looking for other reasons why this happened to you.
Hope this helps.