I was in minor accident mth ago ever since i have had neck and upper spine pain back of head swelling and can't fully turn head right. what could it be?

Need examination: Even a minor accident could have caused some change in your spine and/or neck. If you are having symptoms, see a doctor for a full evaluation.

Better get checked: It could be just muscle strain but it is better get checked to rule out more serious conditions.

Many things: I would talk to your primary care doctor and if they can't solve the problem get a referral to a pain management specialist who does cervical spine interventions.