Im worried that my b.f has lied to me about things that are little but they add up. what should i do?

WE have been together for 6 months and i reall y love him he is amazing but for some reason he feels like he has to lie. when i notice i just give him a look but never speek up. His sis and i are good friends and his problems with past relationships is that he lies constantly. He told me when we first got together that he had a vasectomy and that he could not gat a girl prego but his mom and sis say he has not been fixed. I feel that im prego and i go to the doc tuesday to find out im so worried. if he is ly ing to me how can i spend the rest of my life with a man who has no problem lying to me. i love him unconditionaly but i dont want to be worried that he is lying to me...... What DO I DO?????????