Could you be pregnant if your period is on its regular cycle the first month after sex but miss it next month?

Missing a period after having unprotected sex is a possible sign of pregnancy, but it's not the only reason for a missed period. There are many other factors that can affect your menstrual cycle, such as hormonal imbalances, stress, medications, and changes in diet or exercise.

To confirm whether you are pregnant, you should take a pregnancy test. If the test is positive, it's important to see a healthcare provider for prenatal care.

Here are some additional things to keep in mind:

- If you have a regular menstrual cycle, you are most likely to be fertile in the days leading up to and including ovulation (which usually occurs around day 14 of a 28-day cycle).

- Sperm can live inside the female reproductive tract for up to 5 days, so it's possible to become pregnant even if you have sex a few days before or after ovulation.

- The implantation window is the time when the fertilized egg attaches to the lining of the uterus. This usually occurs around 6-12 days after ovulation.

- If you are pregnant, your body may start producing hormones that can affect your menstrual cycle, causing it to be irregular or even stop completely.

- Missing a period is not the only sign of pregnancy. Other symptoms can include fatigue, nausea, breast tenderness, and frequent urination.

If you have concerns about your menstrual cycle or the possibility of pregnancy, it's always best to talk to a healthcare provider.