Could there be an underlying problem?

We have bn ttc baby#2 for about 21 months now but no joy I am 34 years old and hubby is 29. Our son is 8 years old. We have both bn to the doctors and had sperm count and swabs and everything has come back clear. i have been using temperature charts and opk's but still nothing happening... can I have positive opk's but still not ovulate or low quality eggs? I'm really worried now as I didnt think it would take this long, especially as I fell pregnant the first time whilst still taking the pill. Please help ladies :~(