Hi Nell and welcome to the forum, you have come to the right place! I think its human nature to lapse after having been so good, I did exactly the same. I stuck religiously to the NHS rules at first and lost 1.5 stone but I was motivated by fear and you can only be afraid for so long. I think rather than blithely doing what you are told by the Doc, its much better to come to an informed decision about how to manage your diabetes and to follow your own rules.
Good luck with getting back on track, your determination will serve you well!