Pregnancy is a possibility but stress as well as drugs can cause you to be late on your period so don't get stressed out until you confirm it with a pregnancy test. If you're a week late you will be about two weeks pregnant if you are, and a test should tell you something.
From what you say, I'm picking up that if you are you will keep the baby. Am I right? You're very early in your relationship so I think you're right to be concerned about how your pregnancy would affect it. If you are, it's going to take some very durable and flexible people to handle the enormous change that your relationship with them will undergo.
I suggest you take the test before you start worrying too much. Whether to tell the others you're late on your period is a judgment call you have to make based on how well you know them and what you think their reaction will be and whether you think it will be just needless stress if it turns out you're not pregnant, or if you think it will build honesty and trust.
I agree with above poster that a "what if" conversation is a good idea in any event.
Last edited by Stevenjaguar; 10-09-2012 at 12:32 PM.