What do you advise if i'm on seasonique birth control and had sex 18 days ago. if i ovulated and it implanted would a pregnancy test be positive by now?

Did you miss period?: Conception, as defined by the generation of a fertilized ovum, occurs within day or so of the sex. However, it takes about two weeks for the embryo to make enough HCG to produce a positive pregnancy test. Blood test may be done a day after a missed period. Home pregnancy tests should be done 4-5 days after the missed period. If you missed a period, do the test now.