If your temperature readings vary widely, first make sure that you know how to take your basal body temperature and that you are doing so correctly. Also, consider whether any external factors exist that could be distorting the reliability of your measurements (What factors can distort the reliability of the basal body temperature measurement?) You may also try taking your temperature in a different area. For example, if you've been taking your temperature orally, try to take it vaginally. Many women notice that their temperature readings are more stable when taken vaginally. If temperature fluctuations persist for a couple of cycles, do talk to your doctor, because this may imply ovulation problems.