I came on my cycle a week late, but i took a pregnancy test one positive one negative. what should i do?

Re-test : If negative result came after positive result, the likelihood of a transient "chemical" pregnancy is elevated. Many such silent/passing pregnancies present with similar symptoms. I would suggest repeat testing in one week to make sure the negative result holds. If the positive result came after the negative result, suggest a "blood" pregnancy test to your doctor.