Why Does Semen Surround Penis On Arousal?

Hi I am 21 Yrs old and have a question about a problem that I am having with my penis. I am uncircumcised and have been losing weight to join the airforce. I have been eating nothing but meats and veggies. So far I have lost 40 pounds and it is going great. The only problem is when I get aroused my penis seems to produce semen and gathers at the tip of my penis. The semen has an odor it isnt as thick as when I ejaculate but is the same color. My question is what is going on? I seem to be having wet dream while Im awake. Oh and it sometimes itches from the semen gathering at the tip. whats wrong with me?