My son has a soft lump on the back of his head, he is just 12 days old. It is about 2ins in diameter and it feels like there is fluid in it. He is throwing up after every bottle feed he throws up about half of what he drinks. What culd it be?

You need to get him to the doctor asap and have this checked out.

At 12 days of age you should not be getting info over the internet for something that could be potentially serious.

It may be a soft spot. Baby's have two one on top one in the back but that young you shouldn't risk it , take him to the e.r like she said. My son has a soft spot on the top of his head and I can feel the fluid also but..

it may be a soft spot..

If it were the soft spot, it wouldn't be on the back of the head. Yes, there are two soft spots (fontanels) but neither are on the back of the head where the OP is describing.

It there were a bulging lump on the fontanel after 12 days, this would constitute a medical emergency.