Hi. I've been on 3 x 500 metformin since mid December and have lost 15 Lbs. Some of that is the Metformin, and some is down to a change of eating habits and a daily run.
Even a small cake is deceptively high in calories. Also, 2 stone since August works out at roughly 28 Lbs in 24 weeks, only 1Lb per week which is a nice healthy rate to lose weight. To lose 1Lb you need to take in 3500 calories less - one large slice of cake and a couple of slices of bread daily will easily add up to this over a week, and if you've cut out a couple of biscuits or whatever with a cup of tea, this will mount up very quickly too. E.G. a Penguin bar has 130 calories, 2 finger kitkat 107 calories, Mars bar 280 calories. Even a humble Digestive biscuit (how I miss them) has 70 calories, and if you're anything like me, you cant eat just 1, it would be 4 or 5.
Overall I wouldnt worry, just accept the fact that you are probably eating more healthily overall and your body is adjusting itself to suit. Just start saving for new wardrobe!!