I know a few people who have had persistent bumps on their head Sometimes the size of half a marble) that can be partially scratched off etc. turns out that a lot are related to yeast infection. Good antidandruff shampoo or any yeast infection cream ( a friend was once given vagisil for a yeast infection not down there) helps.
If you have a history of cancer in the family and you are now having headaches and blurry vision. Is it near the nape of the neck? Is the lump superficial like a pimple or boil or does it feel as if there is tissue thickness between touch and the mass. But due to your family history you should go to see your General Practitioner and they will assess you like you deserve.
KNOWING what it is would certainly be better than worrying yourself into a frazzle; I don't understand why anyone would go 2 1/2 years worrying rather than seeing a doctor and getting an answer. Take care of yourself and see someone NOW.