Thank you for your question.
There are several reasons for your problem. Some are related to ongoing infections, hygiene, sexual practices, use of soaps and chemicals, over the counter medicines etc and others related to semen, smegma and urine as well as the foreskin and your ability to clean properly. So it won't be just one thing.
I think it would be best for you to get examined by a doctor specialising in Skin and DVD. You need proper examination and investigations to determine the cause. please also discuss your sexual practices with the doctor so they can help you better.