Diabetes: To change from Janumet to Metformin and see if things improve

My DH is having a really rough time right now. He is having difficulty focusing, he has been really irritable lately, he is drinking alot more (water only), he is eating no stop and his numbers are soaring. He has been under alot of stress and we both are getting worried. Could this simply be a side effect? He takes Janumet 2 times 50/500 and glipizide 2 times 5 mg. He has taken Dualact and Actos both in the past and ended up with depression. At night he sweats all night long and will wake up several times a night. The Gastro dr said he might have Sleep Apnea and that he should be tested for that but not to run off to the gp for that (he has an appointment next month with the gp). Could this be causing the problem? Health wise he is going down hill. He had 4 small polyps removed on Friday. He's already had 2 surgeries in the last three years for abscess drainage (it was to the bone and came up both times overnight). He's really get frustrated (I can't blame him). He is on a pretty good diet plan. I keep him around 45 carbs per meal and that was starting to work. He gets 30 minutes of exercise a day with alternating between strength and cardio. I'm getting concerned because I really don't want him to have to go onto insulin. He doesn't like testing and he's only now taking this more seriously. I would be concerned about him taking the insulin on schedule. I know there are long acting ones but in his job he doesn't always get to eat at the same time. Somedays he doesn't eat at all (usually when he has to go to a job site) or he doesn't eat well. He has a fairly seditary job also (believe it or not he's behind a computer most days and eats while working). All of these I could see being a problem on insulin. Please shead some light. I know I'm not able to control this for him I just need to know that it will be alright and that it could be the meds that are causing this.
We are faxing a request to the dr to change from Janumet to Metformin and see if things improve. Just figured I'd see what you guys/gals say.