For almost all girls, there is the idea that sex accelerates the onset of periods to some extent.
One of the reasons for this is bleeding after sex or during sex, and this combination of sex, blood and your next period date can confuse you.
Even if you know your body really well, it can be tricky to pinpoint the cause of sudden bleeding.
Thus, the question arises: Does sex affect the arrival of periods?
Let us tell you that no, sex has nothing to do with getting your period sooner.
It could be a coincidence or you just had intercourse at the beginning of the first day of your period.
In some cases, it can also be menstrual blood, even though it's not exactly the start of your period.
Kendra Segura, OB/GYN, says that “sex can make it seem like your period is coming faster, especially if you have 'old blood' in your uterus that hasn't completely drained.
That being said, most experts agree that sex doesn't make periods faster.
The only way sex affects your period is if you get pregnant.
Source: WebMD