Hello, and I hope I can help you today. Implantable contraceptives like the Implanon and Nexplanon, even though they have expiration dates, are effective for even a few months beyond that date. This is because the manufacturer is required to post an expiration date that is actually earlier than when the device truly becomes ineffective. When switching birth control methods, hormonal symptoms are very common. Many of the symptoms that we commonly associate with pregnancy including bloating, breast tenderness, moodiness, weight gain, nausea, headaches and others are common side effects of progesterone based contraceptives (like the Nexplanon) and cannot be distinguished from pregnancy. The only way to know absolutely for sure that you are not pregnant is by performing a urine pregnancy test. Modern pregnancy tests are extremely accurate, and will become positive within 10 days to two weeks after conception. However, the reason your healthcare provider did not require pregnancy test before giving you your new Nexplanon is that, because of the reason I explained earlier, you really were not at risk for pregnancy. So the likelihood of your getting pregnant in between switching from Implanon to Nexplanon is close to zero. The symptoms that you are experiencing are likely side effects of your body s adjustment to the new medication, which will likely subside over time. I hope I was able to adequately answer your question today, and that this information was helpful. Best wishes, Dr. Brown