How can we save money?

I'm 16 and pregnant. It's time to start buying things for the baby. I'd been saving up for a car since before I even found out I was pregnant, but once I did find out, I opted out of a $6,500 car and went with a $1,500, since that's about what I had saved. My boyfriend is supportive and he has over $500 in the bank saved for the baby, but I'm just about broke after buying some much needed maternity clothes.

My question is, what can we buy used? Are clothes safe? How many diapers should we stock up on? How many cans of formula (my entire family is lactose intolerant and I'd like to stock up just in case I can't breastfeed). Once I have the baby, I won't be working again until she's in preschool (since all of my money would essentially be going to daycare anyway).

What do we need and what can we get by without?

And no comments on my age, please. I'm sure I've heard them all before.