I have never taken the pill ( I use an IUD), and I don't know the specifics, But I do want to say that getting pregnant at 18 is far from easy ( I know). Having my son DID give me all the purpose in life I would could ever ask for, but it was harder than I ever imagined at times. I have sisters your age, PLEASE, PLEASE, get on a good schedule and take it regularly. You deserve to decide when to have babies, you deserve several more years of living for yourself before learning to be so selfless as a mother is. And if you are already preggers, everything will work itself out, but it is hard to be thrown into a pregnancy when your not ready.
I hope that helps in some way. ( My sister and I just had this same conversation)