welcome
good luck with your dietry changes. tbh i wouldn't go with total radical diet change immediately. rather a couple of wee changes at a time. white to brown bread/smaller portions etc to begin with. your body will likely be used to the higher sugar levels, and bringing them down too quickly can have an effect on focusing on things. that should pass within a relatively short time frame. All carbs all convert to glucose some faste than others with the more complex carbs taking longer to digest wholewheat vs white. a blood glucose monitor can show you some trends of what foods agree with you and which don't.
slow and steady gets you there its a marathon and not a sprint best wishes to the future.