How likely is it to get pregnant when having sex literally right after period?

Not very likely: You are not likely to get pregnant. Your risks of pregnancy are increased if you are healthy, have normal regular menstrual cycles and have unprotected genito-sexual intercourse with a fertile man during your fertile period (about the time of your ovulation). If you do not wish to get pregnant, ask a knowledgeable Gyn for an intrauterine device or a subdermal implant and use condoms too. Be safe.