i had similar problems last year, doctor said it may be the metformin or i could be allergic to wheat,
january i went onto slow release metformin and cut out wheat and overnight my dodgy stomach went away, in may i had a 6 month check up and the nurse put me back on ordinary metformin but i stayed off wheat, within a month the dodgy stomach came back, went back and asked to go back on the slow release and went back eating wheat, at the moment im 95% ok, get the odd dodgy stomach but maybe once every 2 weeks instead of every day,
ive just had another 6 month checkup and i think il be going back as my sugar level is up at the mo so would imagine i will have to up the metformin as im only on 1 a day