What Causes Soreness In Penis?

So after I had sex with my girlfriend, the day after my penis started feeling like if it was sore. Felt like that for about two weeks. Then the tip of my penis head changed color, to this brownish greenish shade. It doesn t hurt when I pee or anything. So my penis has been feeling sore for about 2 months now. And the color change has been for about a month. Is this bad? Or anything serious?