Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice.Masturbation
is very healthy practice. It's natural and normal. It's other way to satisfy our sexual drive.
In the case of masturbation, your fist acts like a vagina. So, don't think negative about it.
Hope I have answered your query. Let me know if I can assist you further.
Dr. Gaurav Patel