Hi, i am 16 years old and was aswell feeling pain in my penis ''base'' after the second erection, not in the tip or everywere else. i do make all the semen come out like by squeezing it, and peeing (or not). and today i found a way to completely remove my pain, its by working out my PC muscle. to find out what this muscle is, its simple. the next time you need to urinate, attempt to completely stop the flow. well the muscles that are working at this instant are the muscles you will need to work out. the way i work it out is simple, simply quickly clench and release your muscle as much time as you whant (or can) after the ejaculation. i did this exercise for maximum 5 minutes and tried to get a second erection and no pain was there. first time in a long time ill say.
by the way, this technique is called kegel exercises. doing often this excercise will keep your penis and its erectional capacities in good shape.