sorry to hear things aren't working out for you. While I would usually suggest not to make big decisions while depressed, being pregnant in an unstable financial situation, so you're going to need to make some important decisions regardless of whether you stay or not...
Firstly you need to stop feeling guilty. DIAC know that a proportion of migrants are going to head home again. Their visa allocation numbers take this into account. If everyone who migrates stayed, there'd probably end up being a shortage of jobs in some professions.
Things that jumped out at me from your post that I would be thinking long and hard about:
Why did you want to move to Australia in the first place? Given the current situation, can you forsee a way for the issues to resolve such that you'll eventually get the benefits you moved here for?
How important to you is your career? If you can't teach over here, are you going to resent the move to Australia for taking that away from you? Do you think you could be happy working in other jobs you'd be able to get without further training?
What does your husband think about all of this? is he keen to stay and try a bit longer or would he be happy to return?
If you do return, what lifestyle would you be returning to? would you be able to get jobs/house/etc or would you be returning to effectively the same situation you're experiencing here in Australia?
Lastly, never is a long time. If you do return to the UK, it could be that in years to come you no longer value your teaching career as highly, or have changed career in the UK, or have saved enough money to be in a far more stable financial situation, such that a move to Australia might work significantly better. There's no shame in deciding further down the line that you want to give it another shot.