Hello, and I hope I can help you today. Birth control pills definitely have decreased effectiveness when you do not take them properly. So, if you have been having unprotected sex and miss more than 2 pills in one month (without backing them up) you do have a chance of having conceived. However, irregular bleeding and pregnancy symptoms are also common when you miss pills, as your own hormone production resumes when you miss more than two pills in a row. So when you resume taking the pill, your body can have high hormone surges, which can result in side effects that mimic pregnancy symptoms. This can also affect the timing of your cycle during the pill-free week, either delaying it or making you bleed differently from your typical cycle when you use the pill correctly. Over-the-counter pregnancy tests are very accurate and will become positive within 10-14 days of conception. So, if you have had intercourse within that window of time, I suggest you perform a urine pregnancy test to rule out pregnancy as the cause of your symptoms. If you do find out that you are pregnant, I want to reassure you that accidentally conceiving while on birth control pills (and taking them during early pregnancy) has no effect on a developing fetus and is not harmful, so you can have a normal healthy pregnancy without concern for birth defects or other problems. I hope I was able to adequately answer your question today and that my advice was helpful. Best wishes, Dr. Brown