A early sign of pregnancy is if your breast are tender and your nipples get darker. But I don't think it will show after a week. Best thing to do is go get a pregnancy test. Doesn't matter what kind I used the ones that are a dollar from the dollar store.
Theres no way to tell at just one week. Wait about 2-4 weeks then take a blood or home pregnancy test. Look out for symptoms which include: nausea and/or vomiting, tender breasts, darkened areola (the skin around your nipple), heightened sense of smell, etc. But remember pregnancy is different for every woman & u may not experience all or any of these symptoms. Some women just have mild symptoms they don't even notice. Best of luck!