I expect that your concern is due to the following. "In a study published in Archives of Andrology, hypothyroidism in men was linked to reduced sperm volume and motility. Another study published in the journal Thyroid connects hypothyroidism to sperm defects. Hypothyroidism can also cause low libido and erection problems. It may even lower key male fertility hormones like testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH)."
If you choose to delay until you are adequately treated for your hypothyroidism, it will take long enough to gradually raise your thyroid med to achieve the following., as described by an excellent thyroid doctor. "Hypothyroid symptom relief was associated with both a T4 dose giving TSH-suppression below the lower reference limit and FT3 elevated further into the upper half of its reference range. " So increases of only 12.5 mcg of Thyronorm will take a while. Better would be to increase by 25 mcg every 5-6 weeks until TSH is suppressed below range. Along with that you will likely find that you need to add a source of T3 to your med to get your Free T3 into the upper half of its range.
Since hypothyroidism is related to not only thyroid hormone levels but also the cellular response, you also need to test for cortisol to make sure it is neither too high or too low. Also test for Vitamin D, B12 and ferritin and then supplement as needed to optimize. D should be at least 50 ng/mL, B12 in the upper end of its range and ferritin should be at least 100.
An average sized person's thyroid gland produces about 100 mcg of T4 and 10 mcg of T3 daily. When you take into account that thyroid med does not absorb 100%, then the med dosage would need to be higher. So with a T4 med like Thyronorm I expect that you would need to get up to about 150 mcg of T4 and see if that got your FT4 to about mid-range, and also see if your body is adequately converting the T4 to T3. Unless you have some kind of heart condition you should be able to raise your Thyronorm dosage by 25 mcg every 5-6 weeks. If the doctor is in agreement then it would take about 3 increases, so about 15-18 weeks. Before each increase you should re-test your Free T4 and Free T3 and TSH levels. Based on a lot of scientific evidence I expect that your Free T3 level will lag changes in your Free T4 level, so at next opportunity you should ask the doctor about T3 med, if needed to raise your level to the upper half of the range. And don't forget about the tests for cortisol, Vitamin D, B12 and ferritin. Very important. If you think you might need to convince your doctor about this, click on my name and then scroll down to my Journal and read at least the one page overview of a full paper on Diagnosis and Treatment of Hypothyroidism: A Patient's Perspective. A copy for your doctor might convince him to treat you as described.