Burning while urinating backpain bending

Burning and feeling of something holding ( like when I tight pelvic floor muscles) or blocking urine ...pain and itching if press area under frenulum and very small rashes there...at last urine dribble or stays in urethra cause burning... whole urethra burning sometimes... bladder pressure burning... I'm stressed and this is increasing it... Sharp BACK PAIN AT EXACT between area above butt and and of back ONLY WHEN BENDING OR STRETCHING MY LEG STRAIGHT UP WHILE SLEEPING... Consulted urologist...he only did a urine test and said u r thinking too much...and still if not satisfied then do sonography What to do? Is this serious? I'm only 21 Any kidney stones and other obstruction? Or prostatitis Or any prostate issue? He told this occurs after 30-40 age.