What Causes Infertility?

i am 27 years old married at 19-11-2010
get pregnant in jan.2011 then spontanous abortion at 6-3-2011 since this time i have regular period every month & no pregnancy occur my investigations are : serum progesteron at day21 of my period it was 8,fsh,lh&prolactin at 3rd day are normal my husband serum analysis is 0000 count&45%progressive motility
i took clomid &nolvadex 3 months with dose 2 times daily for 5 days from the 2nd day of last 3 periods i want to know the cause of delayed pregnancy&other investigations i should do please