What Causes Itching And Burning Sensation On The Penis?

the bottom of my penis itchy it's been going on a little over a week and when I pee I gotten a burning feeling at the top of my penis. I have peed 3 times to day the first one burned but the other 2 never but it's still itchy and the itch is at the bottom where the foreskin pulls back and that line is too. I don't know what is causing it.