Am I Insane?

I'm 17. I'm on birth control, but that's running out about the end of March. I graduate in June. I want more than ANYTHING right now to have a kid with my bf.
I know people will judge and make subtle and not-so-subtle jabs at me because of all of this. But my bf is on board. He's totally cool with having kids. His parents had him around our age.
My question is: Am I insane for literally planning on getting pregnant and having a baby in the next 18 months?
My bf and I decided we'd get an apartment, have a kid, and then get married when I was done trying to work off any excess fat I may or may not have accumulated whilst pregnant and/or breastfeeding so I can be at a healthy weight.
I understand perfectly well that it's a big responsibility. I know I'm not hugely set up in life. I don't care about going to college parties. I feel like this is a good plan for me. I know I can do this. I just hate that I'm going to have to defend myself to my entire family.