Hypo-thyroid may be the issue if your basal body temperature is in the low 97.3-96 F range pre-ovulatory. Temperatures tend to stay on the low side through out the cycle as well.
Hyper-thyroid is just the opposite and basal body temperatures will be elevated throughout the cycle. In the pre-ovulatory stage the temperature may be at 98.0 F range. And post ovulatory may be in the 99.0 F range.
This is not a guarantee - but a possible indication of thyroid dysfunction.
Thyroid problems are easily treated with prescription medications. If you do have a thyroid issue and don't get treatment the result is infertility and possible early miscarriage. Thyroid dysfunction left untreated can also cause cardiac problems too.
If you are put on thyroid meds to balance it and you do conceive, be sure to continue to monitor your thyroid throughout pregnancy. Pregnancy hormones can affect the thyroid and dosage adjustments may be needed. If you are on thyroid medications, it's important to continue taking them through your pregnancy. If you stop the meds all the symptoms of the dysfunction will come back, possibly causing a miscarriage. This is why it's so important to have a preconception check-up with your physician and go over all the possibilities. You will be monitored to make sure your thyroid stays normal the entire time.
Good nutrition is important if you have a thyroid dysfunction. It's especially important because foods such as soy and high fiber can interfere with the absorption of the thyroid meds. You should take your medication on an empty stomach. Go over your diet with your physician.
Likewise if the man has thyroid dysfunction it will affect his fertility. Untreated thyroid in the male causes low sperm count. So it would be smart to have him tested as well!
Diagnosing and treating the thyroid is super easy and does not need to be a fertility problem. Give the treatment a couple of months to balance the thyroid, then your chances of conceiving a healthy pregnancy will be a lot higher. Always work with your physician and take your medication as prescribed.