What causes severe sensitivity and pain in the penis?

? Tight foreskin. A tight foreskin if uncircumcised can be painful with erection, also a tight penile frenum (skin web between head of penis, glans, and foreskin). Glans of an uncircumcised penis can be severely sensitive when retracted if it does freely move back and forth.
Complex answer. There could be a multitude of problems causing these symptoms. An exam is needed followed by other diagnostics. See your local urologist.