My partner and i had unprotected sex 10 days ago but i took a plan b, we had protected sex two days after that, and had protected sex today. i noticed light pink bleeding when i wiped after i pee. is that a sign of implantation or just irritation?

Cannot tell the difference. 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