Wet, cold feeling in the lower left part of my abdomen (stomach) after drinking milk and laying down. What could this be?

Abd symptoms. The symptoms you described are not very intuitive as far diagnosis is meant. Cold feeling is it just discomfort or pain, is it always after milk ingestion? Is there any diarrhea, nausea/vomiting. How long have you had it? These and other points need to have light shed on to guide you further.