You have access to Plan B but no access to birth control?
There are a couple of things you two need to do. Stop relying on Plan B for birth control is the first thing. She is not pregnant this time. However, Plan B is not as effective as birth control pills. Nor is it as effective as condoms and spermicide. In addition, her body is going to get messed up with all those hormones! - I bet her period is late and you two will be stressing out over it.
Don't say 'we aren't sleeping together until she turns 18' - because that probably isn't true. Both of you may have said something similar the first time you got carried away. And it happened AGAIN.
Prevention. Prevention. Prevention. Get condoms (they are at nearly every store around!). Get birth control (there is a family planning clinic - planned parenthood - in every major city in the USA). There is no reason to have an accidental or unplanned pregnancy.