Hi and welcome to HCM.
It sounds like post commotion syndrome and this is usual fater neck muscles pulling and head traumas. What is worring is that it last for 3 months already so i would do further tests includig CT head and neck and eeg. There can be nerve damage
in neck area caused by muslce contusion
or vessel damage as well. SOmetimes the exact cause cant be found. Standard painkillers, muscle relaxants and anxiolytics may help but if symptoms perist you should do tests that i ve mentioned.Wish you good health.