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Your symptoms are very non-specific, meaning they can be an attributed to a number of things, or it could be completely benign. The fact that you are having these symptoms (shivering and sweating) close to your menstrual cycle could mean that it is simply related to your period. Before every period, some women experience different symptoms, and the shivering/sweating may just be the symptoms you experience before your period. The fact that your symptoms were much worse with IVF may just be a reflection of the increased hormones incurred throughout IVF. Be positive, and take a pregnancy test ASAP. Good luck!