Ask the dr if it could be the metformin? The whole time I was on metformin about once a month or so (not connected with periods though) I was ill in the night a few hours after I'd last taken metformin, with terribly bloated stomach (it actually felt hard) which was painful, and then I would be sick after a while, it would be fine in the morning though. This happened once after I started insulin, it made me hypo (because nothing was being digested the nurse said) so the dr said to stop the metformin, I haven't been ill like that again since. The doctor said it was the metformin, but didn't say why it only happened at night, and never after lunch time metformin.