Suggest Treatment For Uncontrollable Post Prandial Blood Sugar Levels

One of my patients is taking Amaryl 3 mg + Pioz 30 mg with Breakfast, Starvog 0.2 mg after Lunch and Metformin 1 gm SR + Pioz 15 mg after Dinner, but not responding as his PPBS is still around 300 mg and FBS is around 200 mg. Should I advise him to take only Sitagliptin + Metformin ? If yes , what should be the dose to start with. Please send your valuable comment.