Pain in penis possibly caused by masturbation?

a couple months ago the tip of my penis started to sting after masturbation. one odd grip that i have used is holding the upper portion of the penis and reasonably (not excessively!!) vibrating/shaking it back and forth. eventually, i went to a local urologist who saw some microscopic cuts on the tip going into the hole (i did not tell him that i believe it is from masturbation; i did tell him that i had masturbated, but that i didnt think that that was the problem due to embarrassment). he tried silver nitrate twice; both times it helped at first, but the issue soon returned. after two more visits, he does not see anything physically wrong with it, but its still bothering me. first of all, i personally feel like the string thing on the backside moved down from the glans a little because the seems a little saggier. also, the line where the two glans meet on the backside has extended further up to the part of the pee hole closest to me. i also feel as though the line in between the glans is now looser. the pee hole is occasionally tender when touched and sometimes tingles. also, after i urinate, drops of urine continue to slowly fill the penis tip for a minute or so after finishing. the upper interior of my penis also feels sore at times. finally, i have not masturbated since the injury and have not ejaculated either. i really worry about ejaculating because of the throbbing and increase in penis size that comes with it. this is not a UTI or an STD, i believe that it is from masturbation. please, if you know anything about the anatomy of the penis and can help me to figure out what could be wrong so that i can better communicate with my urologist and get better treatment, i would appreciate an answer. i would really like to resolve this problem once and for all so that i can live in peace once again. is the issue possibly deeper in the penis than thought? i dont know what to do... please help!