Have you ruled out anything else that happened when your bodily functions first changed? Did you change any type of food/drink? So many things can affect our gut. It may not be the metformin at all.

Otherwise is it possible to take half the amount of metformin?
I have never heard of a p'doc prescribing metformin routinely along side seroquel. Does your general doctor know what is happening? Do you know what your bsls are? Are you actually a diabetic? Might not be a bad idea to ask your general doctor for their advice?

PS I was taking 200mg of Seroquel at night for a long time before I was diagnosed as diabetic. I do wonder about Seroquel and it's affect on our bodies. I still take 100mg of Seroquel but also get my bsls checked. I know I am dribbling on. Hoping you can get some answers and relief.