Sex on periodWatch
To answer your primary concern, you can get pregnant at any time however the risk is low since ovulation normally occurs 10 to 16 days before your period starts. At this moment (assuming you're on your period) you will have a low risk of an unwanted pregnancy.
Discuss with your sexual partner what preferences each of you have pertaining to sexual intercourse. It is recommended to use other forms of protection regardless of the low risk as nothing is ever 100%. Not to mention risk of STI/D(s) assuming none of you are tested yet.
I hope that helps.
You are still at risk of pregnancy and STDs, so take your usual precautions