I have a friend who has taken plan b, has had 1 positive pregnancy test 7 days after sex then a negative test 2 days after. then a negative test 2 weeks later and 5 days after that another negative, shes had cramps for 13 days now, is it pregnancy?

HPT's are accurate about a week after a missed period. The positive test seven days post encounter was most likely a false positive. Has your friend missed her period? If so, have her see her OBGYN since the dates you posted add up to 28 days after intercourse.

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.