Masturbation can be fun, but too much of anything can cause problem. If you constantly work your muscles without rest can cause your muscles to be painful, some times shrink instead of grow. Constantly masturbating without rest can cause your abdominal muscles pain, lower back pain, and even pain in the anal area.
I would suggest seeing a doctor for help, and follow doctors orders will help with the issue you have. But you need to probably manage the time you spend masturbating, as too must ejacaculation can hurt, as the body losses nutrients with every ejaculation. Your body would need time to repair itself.