Tuner - Let me promise you, with Hugh Hefner as my witness, a 20 year old male who isn't sexually active and masterbates only 4 times a week isn't even close to "quite a lot"! According to this quick reference
http://www.nationmaster.com/encyclopedia/Masterbation as a male 18 - 22 you need to start doubling your "monkey" sessions -
just to get to average!! Don't worry, you can slow down when you hit your late 20's and 30's where the average is still up in the 18-20 times a month range!
Obviously if you have concerns about it effecting your health you need to talk to a doctor before starting any new physical fitness regimine (?!) but you are a male at the peak of your testoserone production and EVERYBODY does it. Guilt and shame are dead weight that you carry for no reason. The more comfortable you can get with yourself now the better it will be for everyone involved when you meet that special girl - she's counting on you so don't let her down! Now go buy a playboy!