How can one overcome the difficulty of adhering to prayer, especially with a disease that causes severe itching after ghusl, and the attempt to stop frequent masturbation, and the question about the acceptance of repentance after years of abstaining from prayer and returning to sin?

You must immediately repent from abandoning prayer and masturbation, strive against your lower self, and distance yourself from the causes of temptation. In the case of janabah (definition), if ghusl (definition) causes severe pain, some scholars permit tayammum (definition), although many do not deem it legitimate except for fear of losing a limb or severe disfigurement. It is better to repent to avoid this problem, and if janabah occurs, strive to perform ghusl. If you cannot bear the harm of ghusl or it causes you extreme hardship, then hopefully the opinion of those who permit tayammum will suffice you, but do not abandon prayer under any circumstances.