im glad your bg is now in the 7 range as was worried when you said it was so low.
But I still definatly think that need to go back your gp and discuss your dosage of metformin, my sister is pre-diabetic and she takes metformin but just one tablet per day this is a prevenative measure and it seems to stabilised her bg which is nearly at normal levels now, that said everyone is different and you have to work what is best for you.
I was diagnosed with pre-diabetes in may last year. I had another GTT in feb this year and it was still showing pre-diabetes however I went to my gp a few weeks ago and he decided to retest me even though it had only been a few weeks and I have since been diagnosed type2 sometimes the transistion between pre-diabetes and diabetes can be very quick.
keep us informed and let us know how you get on just make sure to see your GP. take care
Louise