I take 1000mgs of metformin at 7pm. by 12am my stomach is bloated and i feel nauseated. i understand about the diarrhea but why the other? what to do?

Common side effects: You are having typical GI side effects of metformin which affect 20% of people in the first week or 2 of treatment and about 5% long term. If you have recently started, drop back to 500 mg daily which may help and once you no longer have those symptoms you can try 1000 mg again or better yet 500 mg twice a day. Or you might be in the 5% who just don't tolerate metformin