dodgy temps

[Dasharity]

This is my first cycle charting and i didnt start temping till cd13. i have a bbt thermometer.

Is it common to get great fluctuations in your temp, i take mine at 6.30 every morning oraly but it is almost always sleep deprived. although ii am only woken up i dont get out of bed

I thought it might be my thermometer so i took 4 temps in a row before i got up and they where 36.99, 36.21, 36.66, 35.98, shouldnt they be all the same within reason. would the battery be dodgy since its the one that came in it, it says that it should last upto two yrs and i have only had it a week and a bit.

Please if some one can sheed some light on the situation.

Another thing i would like to know is when your temp dips it is the day before O then you get a rise for 3 consecutive days, does it drop after this or does it stay up until af arrives.