I am on my period, (in the middle) and i had sex last night. i think the condom broke. should i get plan b? what are my chances of being pregnant?

Depends: Depends when your last period started and what day you are now. In short, yes you are at risk of becoming pregnant. If you don't want to be pregnant, Plan B is an option.

Risks: I agree with Dr. Namaky. The chances of becoming pregnant are much lower when on period. However, pregnancy is still possible if a female has sex toward the end of her period and period length is long & menstrual cycle length is short.