Hi, im fifteen and a virgin so it isnt a STD or whatever.

This morning, my penis was in a little bit of pain so i checked it out when i got home. I pulled back my foreskin and there was this substance, (possibly semen?), it had a little bit of a green tinge to it too. There is also slight swelling on the top side of the head and painful to touch. What is this and how should i go about it?