A lump on . Under the skin. Help.?

There is a lump on the left side of my . I am just a teen. I have no clue what it is. It is kind of redish and alittle puffy. A tiny bit itchy. It feels like it's a vein that is really big. It's about 1/2 an inch long. Under neath the skin but it feels like it is stuck to my skin (underneath) because it doesn't move. What do you think it is??