So you will come up on the official charts as obese, and your doctor will say you are too, but really, 5 ft 4, and 12 stone, isn't that bad at all! 
If you have been a fair bit slimmer, like 9 stone, then 12 stone will feel HOOOOOJ, but it's not too bad.
I am not sure I take these weight charts seriously anyway, as they say I should be between 8 st 2 and 9 st 10. I am 10 and a half stone (and 5 ft 4,) and look fine tbh (and I feel OK, with no health issues, and normal bloody pressure!) At 8 st 2 lbs, I would look ILL!
These same charts say that my husband should be between 9 st 12 and 11 st 7, and he is a middle aged man who is 5 ft 9 and a half. He would look DEAD at 9 st 12! (He is 12 st 11 and looks great, so where they are getting 9 st 12 from, I have no chuffing idea!!!!)
Not many suggestions for you, except cut the carbs, cut portion sizes a bit, and maybe walk when you can (and cycle and swim.)
It's an ongoing battle, staying slim-ish!!!