Hi, Welcome to Just Answer!
I am an American Board Certified Neurologist (studied & worked in USA) with a vast neurology clinical practice experience. I am familiar with the condition that you have described and can help you with your questions/concerns.
After carefully reviewing all the available details I am considering the possibility of Occipital Neuralgia in you.
It is due to pinching or irritation of the occipital nerves (greater and/or lesser occipital nerves) that supply that area you mentioned and you can experience upper neck/base of the skull pain and/or headaches.
There are myriad causes although not always they are identified during investigations.
History of injuries to the neck area, whiplash, arthritis in the upper cervical spine, repetitive flexion & extension of the spine (the neck part) may trigger this condition, and there are more causes too. If CT of the neck was not done then you need that. Also as I said above investigations may not reveal anything sometime.
Regarding the management; if you haven't tried already the below options then it may be worth trying.
1) A muscle relaxant like Tab Baclofen .
2) Cap Gabapentin
These help with the nerve-pain, you can use ether alone or in combination.
3) TENS (Transcutaneous Electric Nerve Stimulation): With a small device and electrodes minor electrical impulses are applied to the painful area and this might relieve the pain too. TENS may be contraindicated with pacemakrs of certain types, so if you decide to use this please make sure it is compatible with your pacemaker.
4) If these above approaches do not help then you may see a pain specialist and they may try special interventions like occipital nerve blocks.
5) There are still more interventions like Rhizotomy but they are reserved only as last measures.
These are my recommendations and if you are seeking a more elaborative discussion or have additional concerns then please ask further questions.
All the best!