you should be ejaculating. since you are not and i am assuming that you have never ejaculated in three years during masturbation there could be a problem. one possibility is "retrograde ejaculation" - a condition where the semen is ejaculated backwards into your urinary bladder and not out of your urethra. there are other possibilities of course but this cannot be solved on-line. this may not be an issue that can be solved by a your primary care provider so i suggest that you see a urologist.
when i masturbate i only produce pre-cum(clear liquid). so i have masturbated for almost three years now i am 18. when i am masturbating clear liquid will develop from my urethra i assume it is pre-cum. i masturbate for 5-10 minutes normally and i start getting a great feeling building up which i assume is me about to ejaculate. however when the feeling reaches the end i do not ejaculate and my penis stays in an erection unless i stop touching it then it goes down. i have always assumed this was me climaxing.