Hi I have had a very bad jock itch infection.
Hello and welcome to ask a doctor service. I have reviewed your query and here is my advice.
Ketoconazole binds to androgen receptors and thus interferes with testosterone. It can have sexual side effects like decreased libido, impotence, oligospermia but that is usually seen with long term treatment in chronic mycotic infections. I don't think jusr 3-4 weeks of ketoconazole for superficial fungal infections would cause any significant sexual side effects.
Hope I have answered your query. Let me know if you need any more assistance