I'm getting nerve pain in head left side top. What could it might be?

Nerve pain. It can be a simple irritated nerve of the scalp or can be the beginning of a nerve root irritation: neuralgia. Causes are many and varied. Hopefully relieved by the use of the over the counter anti-inflammatory medication like advil or aleve (naproxen). Consult your physician if condition persists. Avoid harsh hair products or direct hot air dryer.