Why Is My Post-breakfast Blood Sugar High Despite Regular Exercise, A Balanced Vegetarian Diet, And Diabetes Medications?

I am 75 yrs male with diabetes type 2 since 26 years. I found my typical sugar is Fasting 100 to 105, pp break fast 160 to 180, pp lunch 160. I take januvia 100 +metformin 500 + voglibose .3 + glimmepiride 1 mg at breakfast, voglibose .2 at lunchtime and at dinner metformin 500 and voglibose 1mg. My HbA1C was 7.4pc 2 months back. I want to know why my pp breakfast is high, despite of my regular exercise 6 km walking per day and simple balanced vegetarian food of about