How fertile can i be after my period?

Fertility post mense: It takes some time for the process of egg maturation after your period to be fertile> usually a week after bleeding ends.

Potentially.: Conception can occur from vaginal intercourse during menses if ovulation occurs early.

Depends: If true period, then unlikely to be fertile soon after. But this is assuming a true period. Some women may have vaginal bleeding in between cycles, and thus may in fact be susceptible to pregnancy after episode of vaginal bleeding if around time of ovulation.