Chance of pregnancy if i had unprotected sex on my period and then took plan b 19hrs after? i finished period as normal and had another 3dys later

Very, very low: If you had sex during your period, then the risk you were ovulating is low to start with. Combine that with the fact you used Plan B in an appropriate time frame to prevent pregnancy and then appropriate sloughing of uterine lining 3 days after the Plan B, the chance you conceived is extremely low. Plan B should not be your primary contraception, though, so if you are going to have sex, talk to dr