I hit my headwhile wearing a helmet. after falling i started crying for no reason and was tired; later i got neck pain. could i have a concussion?

Perhaps, but : The emotional dyscontrol issue may represent some mild traumatic brain injury. See your doctor and if persistent problems get a neuropsychiatric eval.

cervical disc hern: Sometimes cervical disc herniations can refer pain to head and neck. Weight of helmet would put axial load on disc making it worse.

Concussion : Fatigue and mood changes are both signs of concussion. See a physician and be sure to get treated appropriately.