Have you tried a new vial of insulin to check if the old vial is the problem?
It could be the usual diabetes . . . All is well till something changes. We all have to make carb ratio changes and/or basal changes. Sometimes it's weight loss/gain, sometimes illness or extra/less activity. Then of course it could just happen for no apparent reason. It's just diabetes and we've got to deal with it. You'll get there, eventually. If not, ask here again or speak to your DSN.