Thanks for your query.
After over 8 years of trying for conception, you should now consult an Infertility
there are various reasons for infertility
You should have the following tests done after consulting a SPecialist - basic hormonal
profile, blood sugars, thyroid hormone and adrenal hormone tests, blood group
and tests for sexually transmitted diseases, semen analysis
of your husband, basic ultrasound
and pelvic examination for you, and lastly, a tubal patency testing also.
Since the reasons for not conceiving are numerous, it is not possible to tell you whats wrong with one simple answer. Only a thorough workup would tell you that, even then, 30 % of cases of infertility are unexplained ones.