Hi Maz!
First of all - well done on your incredible loss.
And try not to panic... at least you aren't putting any one. Have you looked at your current eating patterns (My Fitness Pal is really good for this) and seen if there's anything you have been over indulging in. Is it more booze? More fat or sugar?... than normal?
Are you exercising? Could you step it up?
Are you still covered by post op care plan? Dietitian chat?
Again, try not to worry I'm sure someone with more and better advice than me will be along soon enough x