The lump on the back of your neck would be a part of your spine.
I don't know why! Go to a doctor!
Well it depends: I have a painless lump on the base of my neck but that's part of my spine! I'm guessing it is the same for you. But if you're really worried and think it is something different, then you should seek out a doctor's advice.
If you are worried about the lump on your neck then please go visit a doctor. A doctor will be able to help you much more than anyone here.
Probably a lymph node.
It sounds as if it could be a growth. You need to consult a physician, who may recommend that the lump be removed by surgery. (It's usually a simple, minor operation), tumor
It could possibly be a cyst. Consult your doctor for proper diagnosis and treatment.
It could be a growth, so have a doctor examine it.
Could be a lymph node.
a turtle neck