The condition you are in is natural result of seeing porno and doing masturbation.I hope you have not injured your nerves by masturbating for 30 minutes at a stretch. You need to take the following steps.
Stop watching porno.
stop masturbating.
Distract your mind from sexual activity.
You can achieve all the above things by doing abdominal breathing. Google the phrase- abdominal breathing. learn this breathing. practice it for 15 minutes twice a day. After a month do male deer exercise, kegel exercise, anal peripheral prostate massage. Google the above exercise to learn them and you may practice gradually. or you may take advice from a doctor.Read messaes from other members to get more suggestions.