What Causes Pain While Passing Urine And Greenish Puss From Penis?

I am suffering pain during passing urine from last 10days, now from last 3 days, i observed pus coming from penis earlier it was white-yellow, now it becomes some greenish shed. What is this ?? is it gonorrhea or chlamydia or something els, pl suggest what i have to do. its very painfull. I am afraid & worried lot.