I do not use any lubrication so i guess it must be vigourous masterbation. Could it be dehydration by any means like if i was drinking beer and then masterbating?
Of course I cannot make a specific diagnosis. But my guess is that you are irritating your urethra, either with direct physical trauma by vigorous masturbation; or that you are getting chemical irritation, perhaps due to whatever you might use for lubrication. In particular, if even the slightest amount of soap gets into the urethra, it would cause exactly the symptoms you describe. As an experiment, you could try masturbating with a condom, preventing any contamination of the urethra (but not a lubricated condom with the spermicide nonoxynol-9, which can cause the same symptoms!). If you still have the problem, it's probably just physical irritation, and you can learn to go easy.
In any case, if you're not otherwise sexually active, it obviously can't be an STD. So that's as far as I can go; I'm an STD specialist, not an expert in details of sexual function.
Good luck-- HHH, MD