Hi, I am having a problem of burning sensation at the tip of penis after masturbation and the tendency to pass urine or stool. It last for half an hour or so. Also, sometimes I am having itching problems under the foreskin of my penis.

See a doctor. It's almost certainly something minor like thrush, but you need to get it checked out and cleared up. If it is thrush, it won't go away on its own.

First off, how old are you?

Second, are you sexually active? If you are do you use condoms? Does your partner have a STD?

It could be that you've just over stimulated or got some grit or what not underneath, goodness knows I have had that happen to me. Clean it out thoroughly and refrain from masturbating for a few days. If it stays go to see a doctor. It could be a number of things. Get a full STI screen.