Ie. Implantation dip, drinking (alcohol), poor sleep, low progesterone, random phantom tww dip with no explanation ...um, there's probably many more but thats all I can think of atm! I wouldn't worry unless you get lots of dips or have quite low temps.
Your cervix moves throughout the month doesn't it? Retroverted uterus' seem very common...so it wouldn't surprise me if the cervix position could vary between women as well.
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