It can be an infection, inflammation, irritation ,tumor or trauma in your reproductive tract. Most of the time it is due to inflammation of the prostate or seminal vesicles. I suggest to you to see a Urologist for an evaluation.
For more information check the links just below:
Click the ACCEPT button if my answer is helpful to you. A BONUS would be encouraging. Please take a minute to leave a positive FEEDBACK for me. If you have more question please feel free to ask. Take care.