What to do if i frequently masturbate.when i do i feel like i'm mentaly ill.what is the reason?

Get good counsel: During the decades after puberty, all male and most female humans enjoy their bodies while alone, up to a few times a day. Only if you're obsessed with erotica to the point of missing out on other good things in life is it a problem. If someone has made you feel like this is dirty or "sick", you have my sympathy. Talk with a few sensible friends and/or your physician &embrace being an adult.

Guilt: Like people in many cultures you undoubtedly heard negative comments about the practice growing up & have embraced the shame it is designed to cause. If you cancel those inputs, and look on it like your body does, it is no different than sex with a partner. If this idea is not helpful, you need to find an unrelated counselor to learn how to deal with it.