Hello, and I hope I can answer your question.
If you have been having unprotected sex and are at risk for
pregnancy (not using birth control) you should do a test to make sure you are not pregnant.
However if you are not pregnant, a lot of other factors can make your period abnormal once in a while. Your ovaries are not a perfect system, and occasionally ovulation is late or doesn't occur, and when this happens, it can make your period come at the wrong time, or you may have more PMS and
bloating than usual, or more or less bleeding.
Stress, travel and weight changes can affect your period.
So pregnancy is a possibility, however it is not the only one. If you are not pregnant, wait a month and see what happens, because usually your cycle will become normal next time. I hope this was helpful and good luck with your situation.