Was supposed to get my period 5 days ago. how accurate would a pregnancy test be now?

Inaccurate. A negative result should not be trusted, and if you don't get your period for the next couple weeks, it should be repeated.

Conception occurs within day or so of the sex. It takes about 3 weeks for the embryo to make enough HCG for 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 the result is negative repeat the test in 4-5 days. Use first morning urine and follow instructions for the test carefully.