During and after masterbation, why my upper part of penis becomes like slippery?

[Volt2002]

I once used to do too much masterbation. Also instead of stroking I squeezed my penis a lot (and specially the top of penis which I liked so much). As once I have got PE and no pleasure in masterbation, I decided to stop masterbation for more than a month. After recovery of PE a bit, I started once a month. But now whenever my penis is erected I feel it to be like slippery (not like before that was a stout feeling), specially when the pre-cum comes out, at that time. During and after masterbation same happens. Also after masterbation I have to give much pressure to urine. I am a 17 year old boy. Plz suggest me whats the problem, cause and remedy.