You may have some allergic reactions to some of the hair products that you use, if you part your hair and look in a mirror (though it may be hard to do), is it red like a rash?
Does it burn when you shower (warm/hot water) or is it soothed when you apply shampoo?
I'd think that the scalp situation is caused by a reaction from something you're currently using or taking that your skin doesn't agree with.
Anxiety from this can definitely cause a headache as well as the pain from the head.
How often is the eyelid twitch?
considering your scalp is on the outside of your head (you've got your skull you must account for) the possibility of a brain tumor is paper thin.
You'd be experiencing much worse... unbearable symptoms had it been a brain tumor... that could effect your motor functions as well as speech depending on the location of where it is.
You must keep in mind that there are so many different parts of the brain that even the littlest of sections control something major in the body.