BBT chart gives a rough idea on estimation of ovulation time. But temperature may vary according to general illness, common cold
, pelvic infection
, systemic disease, change in environment/ place etc.
So, you need to rule out these factors. 1-2 days variation of BBT is nothing so important during period. But you would continue to track down BBT on regular basis.
Kindly consult with your doctor if needed. Good luck.