Any ideas

I’m 42. And got my BFP before Christmas at 13 DPO. I’ve continued taking my bbt out of habit. My normal time for taking my bbt is 6:10 am. Today I slept in till just after 8 am. And my temp dropped...from above 37 C to 36.5 C. I’m slightly freaking out as my temp hasn’t been that low since I got my positive. I am just over 6 weeks. Have my first ultrasound scheduled next week around the 7 week mark. I had a missed miscarriage in April...was suppose to be 11 weeks but baby stopped growing at 6 weeks. Could this temp drop be because of the time difference? (I have no bleeding or spotting)