Hi Jimian
Were your blood sugars very high before you started the Metformin? If your body had got used to being rather high, then coming down to normal levels can feel like you're hypo (even though you aren't), this will settle as you get used to normal levels again.
Does this feeling come when your levels are around 4.1? If so you may be going slightly hypo (below 4). As a type 1 I'm no expert on metformin, but in that situation increasing the dose sounds unwise - check with your doctor. Maybe having started the metformin your body has recovered slightly and become a bit less insulin resistant??
It's good that you're able to test your blood sugars, so many T2s are told its not necessary. If you test when you feel bad and there's a correlation at least you'll have the evidence to discuss with your GP.