I had sex 7 days ago and my period was due yesterday can i take a pregnancy test now? or if not when should i?

Yes: After a missed period is the best time to test!

Right time: 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. Please seek care from a doctor to protect your and your baby's health.