Does having left inguinal hernia surgery cause a varicocele?

It can. If the pampinaform plexus are injured during the repair, it can manifest as a varicocele. This happens infrequently, but not a detrimental occurrence.
Very unlikely. While in theory a hernia repair could compress the testicular veins and cause this. I have never seen it in practice in 15 years, so it is a rare occurrence. Usually the cause is unknown, but abdominal tumors or other types o vascular malformations could be the cause. You should see your doctor for an exam. May need consult with urologist and/or your hernia surgeon.