Had sex during period but as it was ending, been on bc pills for a long time but recently switched and just started new pack of pills. my partner ejaculated in me, what are my chances for pregnancy?

Very low chance: If a woman is consistently taking birth control pills (same time, each day) and has been doing fine on them for more than a month, she is protected against pregnancy every day. That protection doesn't change whether she is on the hormone pills or the inactive placebo pills. She doesn't need to worry much about pregnancy, regardless of when she is having sex, but she can still catch STD infections.