Without a good picture its hard to say, and even with a picture we cant say for certain. It could be a whole host of things, but a picture will deffinetly narrow the options.
I dont have access to a camera. It looks like swollen glands. It is on the very back of its head and both sides of the head are swollen. I can tell that it is two separate lumps because one side is larger than the other and there is a line between the two lumps that separates them (I hope that makes sense)
To be honest it sounds like you're just describing it's head structure. Where the spine starts, right? At the back of the head? That's the structure of the snake's head.