Good afternoon.
Any time of the month there is a chance of becoming pregnant if that is what you are concern about. You just need to remember to be safe. A condom will never provide 100 percent protection. If I was you I would use a condom and talk to your health care provider about getting on birth control of some type.
Birth control can sometimes delay your period, sometimes and sometimes can even stop your period it just depends on the type you are using. As for the sex itself, I know that when I had sex for the first time I was late on my period that month. Though your menstrual cycle changes over your lifetime, and that is normal. Just be safe and speak to your doctor about some birth control methods.
I hope this helped if you have more questions let me know...