If my bf touches the top of my vag with semen on his hands but the next morning i start my period . could i be prego?

No: If you have a normal period after you have intercourse, you aren't pregnant. Consider it a second chance. Next time you might not be so lucky. You should consider going on birth-control pills or some other method to prevent pregnancy. A very high percentage of pregnancies are unexpected. Don't let it happen to you! Best Wishes!

Unlikely: If you started your period and there was no ejaculation of semen inside you, it is very unlikely that you are pregnant.