casein protein and the milk allergy

So we know breads and dairy products often can cause water retention and bloat in some/most people. If I understand correctly, this is because most people have slight allergies to these items. Some have even stated that these when these allergies are acting up, it slows fat loss.

Does casein protein (from shakes) cause the same allergy being as it is from milk? Also, does benadryl counteract these allergies? I use casein before bed, and I usually take a benadryl to help me sleep at night.

I personally haven't noticed additional bloat form the casein (at least not as much as when I am drinking milk regularly) and I think the benadryl may be the reason for this. Or possibly, just because I sleep through the period of time when the allergy is active.

Any thoughts?