OP, you say your mum knows and both she and your boyfriend are supportive. I suggest you show them this thread, and get their opinions again.
As ruby said up thread, go and see your family Doctor. When you are there, I think you also need to talk to him / her about Why you need this baby.
In practical terms, I think you should start looking at the "becoming a parent board" and start adding up all the practical things you need to buy for the baby, at least for the first year and how are you going to pay for it all:
Basics:
Nappies you will need about 200 a month, which according to this site will cost you about $60-70 AUD per month or 800 for just the first year
Will you breast feed, or formula feed (then add bottles and formula - say 4 boxes a month)
Babyclothes - s/he will need new ones every 3 months
Moses basket / crib
Pushchair
Carseat (can your boyfriend drive/ do you have a car?)
Babybath
Highchair
Sterliser
This is just a tiny list compared to the huge amount of equipment babies seem to need. Will you be able to buy it all? You say you want to keep it a secret, but you may need friends and family to lend you things.
Also for yourself, you will need maternity clothes, nursing bras.
Are you prepared for your changing body shape, stretchmarks?