Hi hun, welcome to BB

Glad you're getting started on doing your homework. First things first though, I'm pretty sure that you will have to push your ex for child support, as the government isn't keen on paying for dads who won't stand up to their responsibilities - and you don't want to have to be punished for your ex's lack of care for his child. Besides that, he should be signing the birth certificate as his child deserves to have that legal record and knowledge of his/her parentage, if that makes any sense?
So I would definitely advise trying to talk to your ex about that - if he wants nothing to do with you and the baby, that's his loss, but you and the baby shouldn't be penalised for that - as Counting Days says, he helped make this baby, he should have some part in its life, even if that is purely financial support.

As far as I am aware (and bear in mind I'm definitely not an expert), you will be unable to receive assistance until after the baby is born, but yes, you will be entitled to the baby bonus in instalments (this applies to everybody, not just those under 18, as of January 1 this year). As a single parent, you will also be entitled to the single parent pension, but I'm unsure as to how much this is per fortnight and I could be wrong, but I think the amount you receive also depends on your individual circumstances - and again, I think the amount *may* be reduced if you are not in an agreement with the Child Support Agency and your ex, and not receiving any help from him.
You should also be entitled to Family Tax Benefit (there are two parts, A & B, I think as a single parent you will receive both, but then again I'm not 100% on this), and there are things like Immunisation Allowances and I think a Maternity Allowance (I remember receiving this, I couldn't tell you what it's for or how much it is though).

The best advice I can offer you is to either check out the Family Assistance Office website, or even better (as most of that stuff is barely understandable jargon to most of us!) make an appointment with Centrelink to go in and talk face-to-face with somebody about your options, your entitlements, and how to go about applying for these things - again, most of this stuff you can't do anything about until baby is actually born, so try not to stress too much as you have plenty of time to work things out, but having some knowledge of what you can expect is never a bad thing.

It may also be helpful for you to speak to someone at Centrelink about some form of support during your pregnancy - it's very tricky, but if you have medical conditions that prevent you from working (and I know from experience that it's really hard to get a job once you're showing, an employer doesn't want to waste time and money training you only to lose you in a few months), you may be entitled to some kind of allowance like Youth Allowance or even a disability pension... but again, it's quite hard to access those kinds of payments, especially as a minor and if you have your parent/s around (because you're not classed as an independent so everything goes on what your parents earn etc), so I wouldn't get your hopes up.

Good luck with everything, I hope you're taking it easy and keeping in regular touch with your GP regarding both your pregnancy and your mental health - I've suffered depression and anxiety disorders for years so I know how hard it can be adding a pregnancy on top of all that! It is totally doable though, just try to stay positive and keep yourself surrounded by good people who care about you and will support you. We here at BB are always good for a sympathetic ear and information so don't hesitate to stick around!