Hello, and i hope I can help you today. Nexplanon, as long as it is not expired (which occurs after 3 years) has never been shown to have a pregnancy failure. Therefore, as long as your device has not been in longer than 3 years, you should be completely protected against pregnancy, even if you are having regular unprotected sex. In addition, antibiotics (except certain kinds that are very strong given by IV) have never been shown to actually increase risk of pregnancy while taking birth control- the interaction is theoretical only. Furthermore, the side effects that most people attributed to pregnancy like nausea, bloating, breast tenderness, and mood changes are also common side effects of any progesterone only contraceptive. The reason for this is that the hormone in Nexplanon is very similar to the hormone that is produced by a normal pregnancy. In addition, many women do not menstruate on Nexplanon, which is normal. So you really do not have to worry that you are actually pregnant with the Nexplanon based on your symptoms and with a negative pregnancy test. If you are having side effects you find unpleasant, you may want to discuss changing to an alternative birth control method with your healthcare provider. I hope I was able to adequately answer your question today and that my advice was helpful. Best wishes, Dr. Brown