Couple of things...
To help you understand how glycaside works on your blood sugars I've dug out my records...i started on metformin and glicaside (the first photo. The glycaside dose was upped to max dose by the end of that sheet)
I was then put on insulin, which you can see did the job, shown on the second sheet...don't be put off by the hypos, i was unusually insulin sensitive and they put me on too much insulin)
As you can see, i pretty quckly came down from 20 to 7 before meals (the 7 was after a low carb meal of chicken and salad) on glycaside, but that was as far as it took me.
I am type 1 - adult onset. The glycaside acted quite well, but no hypos.
Obviously your diabetes may differ, but though it may give you an idea on how the medications worked on me, and possibly what one would expect. Possibly.
And a couple of suggestions
1/ i wouldn't take extra food because you fear hypos. Plenty of time to consider that when you actually get into single figures.
2/ i have no idea whats going on, but then, i'm not medically trained, and its a long thread. You need to get those that are medically trained to do their job, partient, polite, but persistant!
3/ ideally, you want to get under 10 as soon as possible. This may be upping your glycaside to the max dose, or insulin, or something else. Again, you need the doctors to tell you. Get on the phone to the gps first thing monday and consider 111 or A and E if ketones get high.
4/ Can't really say what you should do re meals
but personally i'd avoid really carby meals (masses of chips, bread, pizza, bags of sweets, cakes etc).