I had the sh!ts for about 6 weeks on Metformin and lost 18lbs then it leveled off. I used to suck at taking them and then switched to extended release and take all 3 pills at night. Having so much rrhea is a good sign it's working. Switch to extended release (they are a $4 generic at Target Pharmacy) and it will get better I promise.
The constant diarrhea will go away. Having horrendous gas and diarrhea that reeks like burning tires is totally normal on this drug. You'll soon learn what food will have you chained to the toilet and what won't.