Most medications stop working more quickly that they start, so because you are changing between different types you should expect to give it some time.
Although mine was a different situation, when I was put on Sitagliptin and it was only in the third week I saw some benefit from it. I also stopped Metformin for a week and that was enough to see a big increase in my levels.
Here are some more detailed explanations.
Biguanides — which includes Metformin, of which Sukkarto is a modified release brand — work by simply increasing insulin sensitivity. Effectively making the insulin you release work better. As type 2 diabetes is characterized by insulin resistance it is an obvious first choice medication, especially as it has a low risk of serious side effects, a long proven history of successfully helping manage diabetes.
DPP-4 inhibitors (Gliptins) — which include Alogliptin (brand name Vipidia in the U.K., or Vipidomet if combined with Metformin) — prolong the life of incretins in your system. These are hormones released after eating that cause you to produce insulin, stop releasing glycogen (stored glucose), and slow down the absorption of nutrients to make you feel full and stop eating. An enzyme in the body called DPP-4 (dipeptidyl peptidase 4) performs various tasks, one of which is to manage the metabolism by degrading incretins. So inhibiting this enzyme has the effect of increasing your incretin levels and prolonging their effects.
As you can see, the way Sukkarto and Alogliptin work is completely different, they are not like-for-like swaps. So at the moment one is quickly leaving your system, whilst you are more slowly building up the other.
