Has anyone gotten pregnant after their boyfriend/husband got vasectomy?

my fiance just got a vasectomy 6 weeks ago because we both thought six weeks ago that it was what we wanted but now we are both kind of regretting it! he just had a sperm count check and it came back that there were no sperm,.. however my doctor told me that a lot of women get pregnant right after the man has vasectomy even after one check of sperm and that she suggests getting sperm count checked more then once! i was wondering if that is true.. just because one count came back negative is it possible for me to still get pregnant?? has this happened to anyone???