tip of penis discomfort when squeezed

For the past year or so i have had problem with the tip of my penis. I can pin point an area inside of my urethre that is quite sensative and hurts when squeezed. I have been the the doctor, they put me on antibiodics, and i got a urine test. Nothing came back positive. So i went back, retook the urine test, negative again. And the antibiodics did not help. I went to a urologist and he urine tested me. Came back negative. So i gave up. I only notice the pain for a few weeks to days after i ejaculate due to the flexing of my penis. So heres what i think is wrong with me. Nerve damage? There are no signs of an std and im very scared it is something that is undetectable. Please help me. It does not hurt all the time. Just when squeezed. The area is right at the bottom of my head, inside my urethra or tissue.