A couple of things come to mind
- are you unwell or stressed? Both if these things can cause our levels to rise and it is not uncommon to be stressed after returning from a relaxing holiday back to work.
- are you doing less exercise or drinking less alcohol? Both alcohol and exercise can reduce our insulin needs. If your insulin dose was enough on holiday (and assuming you drank and moved more than usual), you may need more on a "normal" day.
- are you correcting your highs? If so, are you using your usual correction factor? I ask because when my levels get high, I become insulin resistant. When my levels are higher than 15, I need twice as much correction and, until this correct works, my basal is not enough.
- are you eating when your levels are high? Due to the insulin resistance, adding extra carbs will exaggerate the problem. I always wait until my levels are below 10 before I eat.
In your position, I would start by reducing my levels using bolus correction (and eating few carbs) and, if they rise again, do a basal test.