I read your whole history, may be
it's a case of sternocleidomastoid strain.more serious injuries may involve swelling .muscle spasm may also occur.
1: Application of hot water formentation ,10/15 min twice in a day followed by volini spray.
2:Avoid other activities like turning your head,bad posture, watching tv, using mobiles..etc.. for min 3 to 4 days..
Next Steps
1: sit or stand facing forward
2:Exhale and slowly turn your head to right ,
keeping your shoulders relaxed and down.
3: Inhale and return to the centre.
4:Exhale and turn to look over your left shoulder.
5:Do 10 Rotation on each side .
Health Tips
if the condition is serious and chronic,it requires more time and application of physiotherapy procedure.. consult me via practo ..