3 weeks pregnant, or 1 week after conception: fertilisation

During fertilisation, a spermatozoon fertilises an oocyte in one of the fallopian tubes to form a single-cell entity called a zygote. This egg, containing 46 chromosomes (23 from the mother and 23 from the father), migrates to the uterine cavity and begins to divide to form a group of cells called a morula.

A small percentage of women experience implantation bleeding, a light bleed that happens about six to 12 days after conception. You may feel implantation cramps as well.