BBT drop at 11 dpo

Victoria

Would there be any reason (other than period coming) at 11 dpo? I was awake with my son overnight and didn’t get a regular nights’ sleep and did take my temp slightly after the normal time but this mornings temp was way below the cover line. Period coming early? I also had my second Pfizer vaccine a couple days ago so not sure if that’s affecting anything. We are TTC baby #2