Hello, and I hope I can help you today. Any woman who is having unprotected sex is at risk for pregnancy, however, if you got your period in September since your sexual encounter, and you haven t had sex again, it is unlikely you are pregnant. Pregnancy symptoms vary widely between women, and many of the same symptoms people associate with pregnancy like irregular bleeding, breast tenderness, bloating, nausea and mood changes can also been used by other hormonal irregularities, such as missed ovulation. In addition, women can have abnormal periods from the stress of worrying about pregnancy. Therefore, there is no way to know if you are pregnant based on symptoms. The way you can accurately find out if you are pregnant is by purchasing an over-the-counter urine pregnancy test and following the package directions. If you are not pregnant, irregular menstrual cycles can be caused by weight abnormalities (both too little and too much body fat), stress, certain medical issues, travel, and even worrying about pregnancy. If your periods remain irregular, I would consider seeing your local physician for an evaluation of your hormones. I hope I was able to adequately answer your question today and that this information was helpful. Best wishes, Dr. Brown