I used the blocking technique last night at the moment of ejaculation, it was not entirely successful this time and a little semen escaped. What concerns me is that for the next half hour to hour there was a BURNING sensation in the urethra towards the tip of the penis - really unpleasant. I don't normally get this and am confident I don't have an STD of any sort.
I did some research online and found the likely cause of it was from drinking a lot of fluids and urinating a lot during the evening before the ejaculation. The plumbing can get a little confused, apparently!