shih tzu

We have an adorable 9 month old shih tzu who has started to change his
behaviour, he has bitten or rather nipped 2 of my younger children over
the last couple of days, I can't believe he has done it. I have taken
him to the vet who has recommended a behaviour therapist which will
cost £176.00 which no way can we afford. The vet has also said
spaying him at the moment would be a disaster for him. He barks at me
now which he has never done before. I have bought loads of books but
it is really hard to decide which bad behaviour caqtegory he falls into
he seems to fall in to them all. Can anybody help???