I've suffered the same dire effect, so to speak, since starting on Metformin about six weeks ago. I've been on three a day for three weeks, which seems to have made it worse. Most evenings I'll go three or four times. This evening it was five or six (I stopped counting), and we had friends over for dinner which only made me feel worse.
I've mentioned this to both my GP and the practice nurse, but both say it's just an unfortunate side effect. I have IBS which only adds to to the problem as I feel like I want to go even when I don't need to. It's getting me down - this evening I cried in frustration.