Had unprotected sex on 2/18 one week before my period is due. took plan b 8 hours later. period is due to come this tues/wed 2/25 or 2/26 and had small bright red spotting last few days. what is likelihood of me being pregnant?

Too soon to know: 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.

Always possible: The egg may still be present and viable one week before your period is due, albeit deteriorating. Pregnancy is still possible so run a pregnancy test if your period is late. P.S. Sometimes women ovulate twice in a month and the resulting pregnancies are called fraternal twins.