Hi, metformin does not agree with everyone if you have been on it for a while and still feeling pretty dodgy you might want to go back to your doctor and ask for alternatives as when I was on it initially it made me feel pretty sick and gave me some stomach aches got it swapped for slow release and was a bit better and then changed to something else completely.
As for feeling better with sugar levels when my diabetes had high levels over 13 and then dropped within the space of a few hours of not eating I used to get symptoms like tiredness and generally achy I was told it was the rapid changes in the bs that cause symptoms similar to before you go Hypo this went away once my levels stabilised and did not fluctuate allot