Neck - Soft tissue symptoms -

tight, strained, burning ,achy feelings in neck muscles, possibly even shoulder & upper back muscles. If those muscles feel rock hard then they are in spasms.

trigger points in those muscles

A good PT, DC & MD (if they feel for it) should be able to feel and tell if soft tissues are a factor.. Sometimes MDs focus on the head injury and overlook soft tissue factors.
Like with whiplash, soft tissue symptoms can show up awhile after the injury/accident.

A friend or family member should be able to help check for trigger points & tight muscles, if those are found then a follow up w/ a good PT is a good idea.