High bg

Obvious stuff first
1) Have you changed over your vials of insulin in case it's gone off?
2) are you injecting into "bad" overused sites?
3) are you coming down with some illness? (eg urine infection might not have much in the way of symptoms but any illness can greatly increase your insulin needs.)

And sometimes you just never know - your blood sugars act up for a couple of days for no rhyme or reason.
If you've got some blood or urine testing ketostix then I'd use them to check you're not going into ketosis.
Otherwise, keep testing and correcting, but be careful not to stack the insulin too much and go hypo (easier said than done).
Do you have a diabetic nurse or clinic you can phone for advice?

H @briony1, I agree with @EllieM, new insulin. new needle and ? urine, ? teeth, ? other infection. Also any stress ??
Talking with your DSN is very important.
Are you just correcting high BSLs or are you also increasing the basal insulin and before meal boluses?
That is part of what your DSN is there for.
Best Wishes.