I cannot give you a clinical diagnosis over the internet unforunately
Your headaches do not seem to have any 'red flags' for a serious headache cause from what you describe
They sound most typical for tension headache, and yes, other symptoms such as lightheadedness, nausea, sensitivity to light etc can occur with tension headaches or what is sometimes termed 'muscle contraction headache'
The neck and head mucles are closely linked to the vestibular system in the inner ear, and brainstem so dizziness and lightheadedness can occur for this reason with headache contributed to by muscle tension in these reasons
It is mroe reassuring that your brain scans have been normal. However you do need to follow with a doctor for the headaches in case they change over time. Also if they become very frequent and disturb your lifestyle, taking a daily preventative medication for tension headaches such as a cyclic antidepressant may prevent or reduce the frequency of headaches.