I Have A Soft, Swollen Area On My Forehead. It's

I have a soft, swollen area on my forehead. It's about the size of my thumb in diameter but oval shaped. It swells up and throbs when I lay down and gives me a severe instant headache. (8/10 pain) but goes away when I sit up and the headache slowly subsides. It's soft and almost feels like a vein, but not like a cyst or acne. It's very painful to lay down. Any idea what this could be or what I should do?