1. You can’t go swimming when you have your period.
There is no reason to not go swimming when you have your period. You can use tampons.
2. You should avoid sex when you have your period.
Sex during your period is fine as long as you & your partner are both consenting.
3. Exercise is bad for you when you have your period.
Exercise is almost always good. If you have pain during periods exercise is always the most effective cure because endorphins (The feel good hormones) are into the blood relieving pain.
4. Your period comes every 28 days
Menstrual cycle varies from woman to woman & from cycle to cycle. Especially when a girl just begins to menstruate. Other causes for irregular periods are stress, lack of sleep, travelling between two zones, strenuous exercise, dietary changes, weight gain or PCOS.
5. If you don’t get your period you are definitely pregnant.
There are many reasons that can delay your periods. A delay in your period doesn’t necessarily mean you are pregnant. Your period could be delayed due to stress, weight gain, Hormonal changes. But if you have had sex & have missed your periods then you should take a pregnancy test.