dear ivarkup, hello.
Common causes of headache on single side are :-
- Cluster headache
- Cervical spondylosis
resulting in pain radiation
towards the effected side.
In your case, it seems that you are suffering from cluster headache as it is unilateral, involves eye region and neck stiffness
can be present after the attack.
can trigger the attack.
You should consult a Neurophysician for medication after getting yourself examined.