I am a healthy 29 yr old male, with no history of medical complications. Since about a year ago, I have been experiencing problems controlling my bladder while masturbating (I've not had any experience with sexual intercourse). In the past, I've always been able to maintain a long period (15-30 minutes) of "plateau" before climaxing in to orgasm. This is the typical chart of sexual sensation one would see in a textbook.
Now, under continual stimulation, I am completely missing this plateau phase and ramp up to the climax very quickly, almost like as if I were going to pee, except that the discharge at the end is semen and not pee. This process lasts only about a minute or two. Additionally, my orgasms are of a much lower intensity. My semen is not uniformly watered down, but instead looks like chunks of semen in a watery base. I'm not quite sure if the water base is urine -- it doesn't smell like it. After orgasm, I sometimes feel like the beginning of a need to pee but when I go to the toilet, I'm unable to pee.
On the other hand, if I stop stimulation right before orgasm, I can pee after the initial feelings subside but the pee comes in trickles. If I then start stimulation again, I will run in to the same problem. The peeing sensation during stimulation persists even after I've repeated this process of stimulation, stopping before orgasm, peeing, stimulation etc. multiple times.
Any insight you may be able to provide would be much appreciated.