Painless vein like lump/swelling underneath foreskin

It will probably resolve itself. If you didn’t use lube you might have bruised yourself a bit. Coconut oil is often recommended for both lubrication and moisturising. It’s also said to help prevent viral, bacterial and fungal infections. It feels good too, though I’m not sure about the coconut smell myself!

It's normal. You might have applied too much pressure and slightly bruised it. Be light on yourself. Apply lube if you like to masturbate. As there is no pain, doesn't look to be a problem

It's gonna suck, but try applying ice and see if there's any change in size. Is the lump "squishy" or firm/hard? 

Is it mobile (does it move under the skin) or is it stationary? Is there any pain? 

Firstly, it's extremely unlikely to be anything serious. Cancer of the penis (which everyone jumps to when they see a lump) only occurs in the head, with an open sore that leaks fluid, blood. This is not the case for you. It might be some swelling of the under tissues, as you have about 3 layers of soft tissue inside the penis with nerves and blood vessels twisting and turning through them. It's likely aggressive masturbation may have broken a vessel, or separated the tissue to cause fluid to leak into a pocket in the topical skin. 

Give it a few days/weeks and leave it alone. Don't masturbate at all if you can help it. Report back with your findings if you feel like it in a couple days or if there's any change. I have a node a bit lower on the shaft in the remainder of my foreskin that's been there for 15 years. It's gotten smaller, but never fully gone away. The penis is a weird part of the body, and occasionally you'll get nodes, lumps, and bumps due to scar tissue, bulging veins, etc. 

If there was intense pain and open sores, bruising, etc... I'd suggest a doctor's visit, but I'm not a professional.  

Anyone else have input on this? It's subsided but still not gone. It feels like there's a bulging vein inside the skin.

I've been going through the same thing for the past few months. It comes and goes. I thought it was Mondors disease, so I went to a urologist today and he said it was a blood clot. He said to stop masturbating and try warm compress. I'm currently freaking out. Has yours disappeared by now?