Hey Stephen, only just saw this....
I think it depends how you are writing the story. If the story is in the first person, as in 'I went to the doctor's' then you can use 'don't and it's'... And stylistically it is up to whether you use it in third person.
And as an aside, for anyone who's reading this and doesn't know - If you are using 'its' as if something belongs to it, then you never use a apostrophe. For example:
The badger ran into its hole
Tha sandwich had ketchup on its crust.
'It's' only means 'it is'.
Hope that helps.
I'd say, as long as all the apostrophes are in the right place, use the abbreviated forms if that is how you hear it in your head. Sometimes the full versions sound a little stilted in narration.
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www.fabulousmother.co.uk
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www.fabulousmother.co.uk