Surgery can lead to problems with absorption of B12 and also lactose intolerance. Your body does sound like it's sending some strong anti-lactose signals.
Or it might be lactose and/or the stuff in your shake and bake, which has milk, MSG (a neurotoxin):
"Enriched Wheat Flour (Wheat Flour, Niacin, Iron, Thiamin Mononitrate [Vitamin B1], Riboflavin [Vitamin B2], Folic Acid), Wheat Flour, Monosodium Glutamate, Salt, Garlic*, Sugar, Buttermilk*, Onions*, Partially Hydrogenated Soybean And Cottonseed Oil, Contains Less Than 2% Of Parsley*, Natural Flavor, Milk, Dextrose, Yeast, Caramel Color, Maltodextrin, Spice, Cream, Silicon Dioxide (Anticaking Agent), Modified Food Starch, Lactic Acid, Vinegar Solids, Butter, Whey Protein Concentrate *Dried"
If you have allergies, you might also be sensitive to the additives in processed foods like Velveeta and Shake & Bake.