I think you need to go back to the doctor, they can either get it through for you as a PBS or prescribe something more affordable!!!

In the meantime, definitely get yourself onto a good probiotic.

Here are some things that I have learnt about thrush/mastitis:
Absolutely do not use disposable breast pads - get some cloth ones or even just make do with squares of clean flannelette folded over a few times. Change them rigorously often and wash them in hot hot water. Same goes for bras.

Watch how much cream you put on your nipples, sometimes it just keeps the skin soft and makes the cracks worse.

If the thrush treatment is not working, use antibiotics AND thrush treatment at the same time. Sometimes the symptoms are similar and you need to do both at the same time to "kill" it.

Get your dr to take swabs/cultures - you may need a different medication. I found the daktarin really irritated my nipples and ended up using a cream called NIlstat (washed off before feeds).

Most of all, if you haven't already, speak to someone who can give you good attachment & positioning advice. This might be a lactation consultant, a breastfeeding counsellor from the Australian Breastfeeding Association, or a trusted midwife. They may be able to give you more tips re the thrush as well.

Most of all, give yourself a big pat on the back! You are doing an awesome job to keep feeding even though you've had troubles with it! It's one of those things, suddenly one day you realise it's not hard and it doesn't hurt any more! Good luck, let us know how you get on.