I Have A Very Painful Protrusion In The Shaft Of

I have a very painful protrusion in the shaft of my penis. It appeared during quite normal masturbation a few days ago. It feels like a very hard vein, but it seems to be quite deep, only detectable by touching it. It becomes much more obvious when I have an erection, and the "vein" sticks out more, also stretching very painfully along the shaft. I can feel it run sideways near the base of the shaft, then run straight up and sideways again further along. The pain is a constant ache, worsening depending on the position of my shaft throughout the day. It gets quite severe when I have an erection, especially if I try to pull my erection down, when it reaches about 7/10, pretty close to agonizing. Based on what I've found so far, it's most likely a clot. I've been trying to wait to see if it will clear up, since it's only been 3 days, but the pain is very limiting and I'm wondering if there's anything else I should do. This is getting in the way of sex with my girlfriend and masturbation and I'm hoping there's something I can do to relieve the pain. If there's anything I can get or do that will help this, please let me know.