Wow, deja vu. I'd swear I heard Guido's words someplace before.
I agree with all he has to say and would like to add a couple things.
This forum is a valuable source of information for all ages. HOWEVER, it is not a substitute for having open and honest communication with your PARENTS. I know it's tough, (just last night my 9-yr old son asked me what a tampon was) but as a parent I can tell you that our love is unconditional for our kids. We are much more receptive of the idea that a teenager would come to us to discuss questions about relationships and sex, than we are "Mom, Dad, I think I'm (or my girl friend's) pregnant," or taking you to the doctor for a course of penicillin.
Despite all of the great advice and suggestions posted here, there are still occassional posts under the general topic "Could I be Pregnant?" Please understand that no matter how careful you are and how many precautions you take, boyfriends and girlfriends will still count the days to her period.
Ask questions, become informed, but simply because you've read alot about swimming, that doesn't mean you're ready to jump into the surf. Be knowledgeable, but be smart with that knowledge.