I hope your dad is seeing an endocrinologist and not just a GP. Glucophage is usually a first line of defense in pre-diabetes and may have been prescribed for your dad for just that. I suspect however that your dad has been taking his pills now for a couple of years but has no clue as to what his blood sugar really is. This is not a criticisim as most "pre-diabetics" just take their pills and aren't required to monitor their BS outside of Dr's visits. The reason I am guessing all this is that the severe abdominal distress and the night sweats are indications he has a full blown case of out of control diabetes (frequent urination and thrist are also signs).
Again I may be wrong on this, but someone really needs to test his blood sugar and find out where he is. Im am also guessing that the doctor simply took him off the glucophage but didn't do a finger stick or a blood test to see where his blood sugar was. If this is the case, its a very simple test and may reveal that your dad needs more meds that he's been presecribed!