hi,thanks for query.What I understand by secondary infertility
means you already had one child and having difficulty in getting another.In medical terms this is known as secondary infertility.Once you are pregnant the major causes of infertility are ruled out.This time the cause could be some hormonal
imbalance,bad semen quality,some uterine problem etc.Please discuss this with your doctor and get your thyroid
checked.He will suggest some investigation to see for ovulation and other things.If everything is normal you can still conceive with low sperm count
with the help of assisted techniques.
wishing you all the best.