Google abdominal breathing. Learn it, practice it for 10 minutes twice a day When ever you have unwanted arousal use this breathing this will calm you. For rough sensitive glans, use lidocaine cream or ointment. It is anesthetic. It will relive your pain.
It seems you have a very rich nerve network around your penis. You shouldnt feel down about it because there are lots of men ( especially circumcised ) that have the opposite problem. They dont feel a lot down there and believe me that is more frustrating. The semen is precum that comes out due to spasms of the perineal muscles that happen involuntarily due to sexual arousal. I understand your concern but this sounds completely normal. You have to expect this to calm down as you grow up especially after 28. After this it will only get better as your manhood hormones will settle down.