You won't be aware of it yet, but you've just become pregnant – congratulations!
Once the egg is fertilised, it travels along the fallopian tube and embeds itself in the wall of the womb (uterus).
It starts to produce a hormone called ‘human chorionic gonadotrophin,’ which stops you having a period and shows in your urine - this is what home pregnancy testing kits can detect when you miss your first period.