The egg (sometimes two, if you’re having fraternal twins) travels down your fallopian tube in the direction of your uterus. If you’ve had sex, sperm are moving upwards through your cervix and uterus.
For conception to occur, a sperm must burrow through the outer layers of the egg to the very middle. This process usually happens in the fallopian tube.
If it does happen, you’re pregnant.
Your progesterone levels increase now. This hormone lets your body know you’re pregnant, causing the endometrium to build up its nutrient supply, which stops you from having your period.