I had light bleeding for an hour but period not due, and mild cramping. ovulation test negative. day 13 of cycle. possible implantation bleeding?

May be: Implantation bleeding is not a reliable sign of pregnancy. Conception, as defined by the generation of a fertilized ovum, occurs within day or so of the sex. However, it takes about 2-3 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 the result is negative repeat the test in 4-5 days. Use first morning urine and follow instructions for the test carefully.