When can i stop taking pregnancy tests and assume the negative is accurate? im trying to figure out if i had implantation bleeding or my period?

If the properly done test remains negative 4 weeks after exposure, I would consider that long enough to rule out a false negative.

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.